cleanup: get rid of most "import *"

Apply script generated with the following hack:
(
hg loc '*.py'|xargs pyflakes-2 | sed -rn "s/([^:]*):.*'(.*)' may be undefined, or defined from star imports.*/sed -ri 's,\\\\<\2\\\\>([^=]|$),XXXX.\2\\\\1,g' \1/gp" | sort -u
hg loc '*.py'|xargs pyflakes-2 | sed -rn "s/([^:]*):.* undefined name '(.*)'$/sed -ri 's,\\\\<\2\\\\>([^=]|$),XXXX.\2\\\\1,g' \1/gp" | sort -u
hg loc '*.py'|xargs pyflakes-2 | sed -rn "s/([^:]*):.*'(from .*)\.([^.]*) import \*' used.*/sed -ri 's,\\\\<XXXX\\\\.,\3.,g' \1/gp" | sort -u
hg loc '*.py'|xargs pyflakes-2 | sed -rn "s/([^:]*):.*'(from .*)\.([^.]*) import \*' used.*/sed -ri 's,\2\\\\.\3 .*,\2 import \3,g' \1/gp" | sort -u
) | grep -v kallithea/bin/kallithea_cli_ishell.py > fix2.sh

tests: add missing tests for closing and deleting pullrequests

Delete and close of pull requests was recently found broken and fixed in
commit 56233b874eba.

Add some tests that would have detected the breakage automatically.

tests: remove tests of UI notifications

This commit is part of the removal of the UI notification feature from
Kallithea, which is not deemed useful in its current form. Only email
notifications are preserved.

tests: test status change in comments and pull requests

Status changes when commenting was not yet covered.
This commits adds the basic logic, but is not full coverage.

tests: rename test_changeset_comments to test_changeset_pullrequests_comments

As the scope of this file now is both changeset and pullrequest commenting,
the filename should change as well.