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
removed link and snippet plugin
typo in requirements
Merge branch 'develop' into link-remove
tests passing but not working yet
Add utility to get alpha insertion point in sub-menus

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Merge branch 'develop' into link-remove
lazy choicefield
Add a test for get_alphabetical_insert_position()

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Fix for case where new item should go at the end

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Passing test

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
Tighter tests, better fix for condition when new item will sort to the end

Signed-off-by: Martin Koistinen <mkoistinen@gmail.com>
upated requirements
updated requirements
removed new migrations
updated locales
Merge branch 'develop' of github.com:divio/django-cms into develop
updated docs
remove the stacks package