Added signal which is fired when server needs restart

As we all know, adding, removing or changing apphook pages requires a
server restart. Until now, the maintainer/content-editors of a site
had to do and detect this manually.

I propose we add a signal ``cms.signals.urls_need_reloading`` which
fires when the CMS detects the server needs a restart.

This signal is just sent by the django CMS. The core itself does nothing
when this signal is sent. However it allows developers to write custom
listeners to that signal that take an appropriate action in their
envirnment.

For some common use cases, there might even be generic implementations
(outside djagno-cms core) which solve this issue (eg killing os.getppid
in single-server gunicorn systems).
restored Python 2.5 compatibility
fixes #2482
cleanup
tests added
fix tests
skipping databases
skipping fix
skip unless wrong import
fuzzy int added
Merge branch 'develop' into fix-2482
Merge branch 'develop' into fix-2482
#2516 : add default children for default_plugins of placeholders configured in settings.py.
fix querie numbers
Merge branch 'develop' into fix-2482

Conflicts:
	cms/middleware/toolbar.py
	cms/tests/toolbar.py
changed color to red and fixed tests
other querie numbers on server
upped queries
test tree view queries and optimize them as well
increased allowed queries