auth_ldap: fix interpretation of LDAP attributes in Python 3

The python-ldap module returns the LDAP attribute names as strings, and the
attribute values as arrays of bytes, e.g. for email:

'mail': [b'john.doe@example.com'],

See https://www.python-ldap.org/en/latest/bytes_mode.html, particularly:
https://www.python-ldap.org/en/latest/bytes_mode.html#what-s-text-and-what-s-bytes

Due to a missing conversion from bytes to unicode for the attribute values
obtained from LDAP, storing the values in a unicode field in the database would
fail. It would apparently either store a repr of the bytes or store them in
some other way.

Upon user login, SQLAlchemy warned about this:

.../sqlalchemy/sql/sqltypes.py:269: SAWarning: Unicode type received non-unicode bind param value b'John'. (this warning may be suppressed after 10 occurrences)
.../sqlalchemy/sql/sqltypes.py:269: SAWarning: Unicode type received non-unicode bind param value b'Doe'. (this warning may be suppressed after 10 occurrences)

In PostgreSQL, this would result in 'weird' values for first name, last
name, and email fields, both in the database and the web UI, e.g.
firstname: \x4a6f686e
lastname: \x446f65
email: \x6a6f686e406578616d706c652e636f6d
These values represent the actual values in hexadecimal, e.g.
\x4a6f686e = 0x4a 0x6f 0x68 0x6e = J o h n

In SQLite, the problem initially shows differently, as an exception in
gravatar_url():

File "_base_root_html", line 207, in render_body

File "_index_html", line 78, in render_header_menu

File "_base_base_html", line 479, in render_menu

File ".../kallithea/lib/helpers.py", line 908, in gravatar_div
gravatar(email_address, cls=cls, size=size)))
File ".../kallithea/lib/helpers.py", line 923, in gravatar
src = gravatar_url(email_address, size * 2)
File ".../kallithea/lib/helpers.py", line 956, in gravatar_url
.replace('{email}', email_address) \
TypeError: replace() argument 2 must be str, not bytes

but nevertheless the root cause of the problem is the same.

Fix the problem by converting the LDAP attributes from bytes to strings.

cleanup: minimize use of lambda expressions - we have 'def' for that purpose

Fix some flake8 warnings "E731 do not assign a lambda expression, use a def".

py3: remove safe_unicode in places where it no longer is needed because all strings (except bytes) already *are* unicode strings

(The remaining safe_unicode calls are still needed and can't just be removed,
generally because we in these cases still have to convert from bytes to unicode
strings.)

auth: move 'active' handling out of the individual auth modules

The 'active' flag in the Kallithea user database is very fundamental and should
not be specific to auth modules. Modules should only care about whether the
user is active in the external authentication system.

user_activation_state is thus removed, and 'hg.extern_activate.auto' is now
consistently checked for all kinds of external authentication.

auth: drop active_from_extern from internal auth API

Modules should never auth a user if the auth source knows the user is inactive.
Also, it is too late and unreliable to disable users when they try to log in.
There is thus no need for this concept.

Only the crowd module had some traces of actual active_from_extern usage. The
'active' flag for crowd users was fully controlled from crowd. Now, Instead,
just let crowd reject authentication of users that are inactive in crowd, and
leave the internal Kallithea 'active' flag under admin control.

auth: change default LDAP to LDAPS on port 636 - insecure authentication is kind of pointless

This will only change the default value for new systems. Existing installations
will keep using whatever value they have in the database.

auth: prevent LDAP query language injection of usernames

This could cause odd LDAP queries that could fail but couldn't give access
without a valid user query and credentials. It thus had no security
implications.

auth: make ldap OPT_X_TLS_CACERTDIR configurable

A location was hardcoded. The location was wrong for many systems and prevented
actual TLS from working. Also, it should not be necessary with modern Pythons.

For some reason, instead of removing it, we now decide to expose it to the
user. Choice FTW!

cleanup: fix 'try ... except ...' formatting missed in d69aa464f373

Examples spotted by Jiří Suchan <yed@vanyli.net>.

Correct licensing information in individual files.

The top-level license file is now LICENSE.md.

Also, in various places where there should have been joint copyright holders
listed, a single copyright holder was listed. It does not appear easy to add
a link to a large list of copyright holders in these places, so it simply
refers to the fact that various authors hold copyright.

In future, if an easy method is discovered to link to a list from those
places, we should do so.

Finally, text is added to LICENSE.md to point to where the full list of
copyright holders is, and that Kallithea as a whole is GPLv3'd.

Second step in two-part process to rename directories.
This is the actual directory rename.