tigefa4u projects Trac

Simplify the implementation of the `trac.core.implements` function (no more frame hacking).

Genshi branch: ported the project index. Custom Clearsilver indexes are still supported, but the ''default'' index is now a Genshi template.

WebAdmin: fix #3680 by adding a date format hint for adding milestones and versions

`get_datetime_format_hint` assumed a 24 hour clock, this should also support AM/PM times

Genshi branch: now works with [genshi 299].

Prepare migration from Markup to Genshi

Markup branch: migration of the Wiki module finished (done the ''confirm delete'' mode).

Finish to make unit tests more robust in case there's a global trac.ini.

Actually, there were a lot less remaining cases than I initially thought,
as lots of `from trac.config import Configuration` lines were useless.

Closes #3700.

Made unit tests more robust in case there's a global trac.ini file around.
- all the tests that are getting their config settings from `trac.test.EnvironmentStub` are now insulated from the global trac.ini.
- the `trac.tests.config` tests are also insulated
- ... but there are remaining uses of Configuration in other tests that have not yet been insulated from the presence of a global trac.ini

Related to #3700.

IRequestFilter fixes:
- update documentation to make clear that only `post_process_request`
should be used to modify the `req.hdf`
- always try to apply filters on the way out, even in case an error
is detected and rendered.

Should fix #3655.