tigefa4u projects Trac

`versioncontrol` sub-system refactoring: `LogModule` was extracted in its own `log.py` file. The common utility functions have been extracted as well in `web_ui/util.py`.

Follow-up to r2110 (fixing the wiki unit tests)

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.