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
initial import and merge
Fix reload after editing models on the frontend.
Adds parameters to CMS.Modal and CMS.Plugin to handle the different cases.
Merge pull request #2461 from yakky/feature/fix_edit_model_reload

Fix reload after editing models on the frontend.
redirectOnClose Hotfix
Merge pull request #2462 from yakky/feature/hotfix_redirect_on_close

redirectOnClose Hotfix
Fix bug whereby the side-frame show/maximize/close controls wouldn't show if the sidebar was hidden and the page was refreshed.
Merge pull request #2466 from igloox/fix_hidden_sidebar

Fix bug whereby the side-frame show/maximize/close controls wouldn't sho...
publisher tests working... hurray
onClose and redirectOnClose are mutually exclusive
Merge pull request #2469 from yakky/feature/fix_reload_close

onClose and redirectOnClose are mutually exclusive
Refactor show_editable_model. Add show_editable_model_icon that adds an icon attached to model editing.
CSS edit for show_editable_model_icon
Edited extending_cms/extending_page_title.rst
Merge pull request #2470 from timgraham/extending_page_title

Edited extending_cms/extending_page_title.rst
Specified file name of toolbar extension.
Merge pull request #2472 from timgraham/extension_location

Specified file name of toolbar extension.
Fix js Style
Fix js Style