scripts: fix crash from comparing integer with empty list

Fixed by using year 0 as default for contributors without any years.

scripts: in regexps, use + when we actually want to make long matches instead of empty

Greedyness seems to have changed with Python 3 and it is less forgiving and
would happily make empty matches everywhere.

scripts: use plain import of contributor_data

Relative import failed with:

Traceback (most recent call last):
File "scripts/update-copyrights.py", line 45, in <module>
from . import contributor_data
ImportError: attempted relative import with no known parent package

Fixed by backing out changeset 2786730e56e0. The pytype problem can be solved
differently.

py3: switch to use Python 3 interpreter, temporarily leaving many things very broken until they have been migrated/fixed in a reviewable way

Bump Mercurial minimum version to 5.2 - the first version that claim stable py3
support.

scripts: use explicit relative imports of contributor_data

Avoid any ambiguity ... and avoid pytype failing to find
scripts/contributor_data.py when scripts isn't in sys.path.

scripts: extract contributor data out of update-copyrights.py

... to allow re-use in other scripts, like shortlog.py.

update-copyrights: fixup double entry for Lars Kruse and regenerate

Caused by translation commit bb62416296db.

make-release: import version and copyright updates from default branch (dba4e770d4b6)

make-release has been improved on the default branch in commit dba4e770d4b6,
and that version of the script also almost works on stable.

There are some parts we don't have in stable branch: dev_requirements.txt,
run-all-cleanup, and a working dist file content check:

The MANIFEST.in file on the stable branch is not complete.
Most of the missing entries could simply be added
(.travis.yml, requirements.txt, tox.ini, and scripts/*) but there is one
problematic entry: kallithea/i18n/en/LC_MESSAGES/kallithea.mo.
In the check command, all .mo entries are filtered out, causing a remaining
diff for the English .mo.

As that file has been removed on the default branch already, and the missing
entries are not important for the release anyway, simply drop the check
for now.

update-copyrights: adapt email of Thomas De Schampheleire

Normalize all contributions of Thomas De Schampheleire to @nokia.com.

scripts: add update-copyrights.py

This script will automate how the current attribution and copyright listings
are generated, thus also enabling it to be maintained from repository history
in the future.

This doesn't change anything about who has or hasn't contributed or deserves
credit, it just does a best effort attempt at maintaining existing attribution
we inherited and automating it going forward. The automation might expose
existing problems - they should be fixed by adding or removing exceptions in
the script.