tigefa4u projects Trac

Follow-up to r2110. I knew I was going to forget something...

only use the !PlainTextRenderer to render textual mimetypes (fixes #1920)

New draft watermark image for wiki preview.

Make sure the pubDate is properly formatted in report rss feeds. Closes #1939.

`versioncontrol` subsystem refactoring:
* Version control related web UI modules moved in the `trac/versioncontrol/web_ui` subfolder
* main renamed to api, to be consistent with the other subsystems.

* Use wiki model class to implement the `wiki remove` command in [wiki:TracAdmin trac-admin].
* Auto-complete wiki page names on `wiki remove`

Treat some file format as binary, even if the binary detection heuristic fails.

Those files can be considered ''semi'' binary, as they are basically non-human readable
(PDF, PostScript, RTF), but the link to the ''Plain Text'' alternative format is nevertheless
made available for those who really want to look at it.

Follow-up to [2101] which removed the credits information (?). Those changes where needed in order to fix the unit tests.

Edgewall's Trac can now also render its own Wiki formatting for files stored in the repository. Let's make the set of default wiki pages benefit from that feature. That way, eventual formatting errors can be spotted directly from the main repository.

Added a slightly more user-friendly concurrent wiki editing detection. This also closes #1739.