Initial commit of the new Radicale extension.
A piece of refactoring.
Better tabforms.
wip: Form to define calendar access rules.
Merge branch 'master' into feature/radicale

Conflicts:
	modoboa/extensions/admin/forms/account.py
wip: Radicale extension

Access rules definition works!
Merge branch 'master' into feature/radicale
wip: radicale extension.
wip: radicale extension.

Permissions.
wip: radicale extension.

Rights file generation.
wip: Radicale extension.

Check permissions and generate owner access rules.
Merge branch 'master' into feature/radicale
wip: Radicale extension.

Graphical improvements.
wip: Radicale extension (#574)

Enable search form + code refactoring.
wip: Radicale extension #574

New option to control calendars adminstration.
wip: Radicale extension #574

Unit tests.
wip: Radicale extension #574

Properly init extension.
Run radicale extension tests.
New feature: check for new versions.

fix #551
Early imports can be dangerous :p

see #551