Remove support for logbook.

If you were relying on this feature, it should be quite easy to
implement it in a third-party panel, and we'll reference it in the
documentation.

Fix #478.
Merge pull request #487 from aaugustin/remove-logbook

Remove support for logbook.
Stop sharing unsafely a context dict across threads.

Panels that need to share data with other panels shall do it through the
record_stats / get_stats API. Statistics are automatically pushed to the
template context.

Fix #450.
Record SQL from executemany.

Fix #293.
Also record SQL from callproc.

I'm not sure anyone is using that, but it's in the DB API.

Fix #293.
Fix JS regression in the template panel.

It was introduced during last week-end's large renaming.
Extract output of context processors instead of recreating it.

Also include context processors explicitly passed to RequestContext.

Fix #353.
Fix instructions for installing the dev version
Reduce the risk of circular imports.
Provide a solution to prevent monkey-patching the settings.

This is necessary to work around extreme cases of circular imports.
We really need to reverse URLs at import time and this isn't always
possible.
Small documentation improvements.
Fix regression from last week-end's massive renaming.
Review translated strings.

- Include trailing colons inside translated strings because some
  languages (eg. French) need a space before the colon.
- Normalize capitalization (title-style didn't seem warranted and looked
  weird in some cases).
- Normalize quotes (not very useful, but we had a random mixture of
  single and double quotes).
- Remove msgstr from the English po file because they're identical to
  msgid by definition.
The .po files are now wrapped.
Pointing to the 'master' docs creates too much confusion.
Added staticfiles panel class.
Actual show the number of used static files in panel title.
Another pass over the staticfiles panel.

- adds some docstrings
- adds some basic tests
- adds the staticfiles panel to the default list of panels
- fixed a pluralization bug in the template
- refactored some things into own methods for easier testing
Use django-discover-runner on older Djangos.
Added the staticfiles panel to the docs.