wip: big refactoring

Moving files.
wip: Big refacto

The admin application is now a true extension.
wip: Big refacto

Top menu is back.
wip: Big refactoring.
wip: Big refactoring

Limits extension OK.
wip: Big refactoring

autoreply extension OK.
wip: big refactoring

stats extension OK.
wip: big refactoring

Webmail still needs work.
wip: big refactoring

* sieve extension still needs work
* auth application removed
wip: big refactoring

Webmail template tags.
wip: big refactoring

amavis extension still needs work.
wip: big refactoring

old userprefs application removed.
wip: big refactoring
Useless import removed.
Merge branch 'master' into refactoring

Conflicts:
	modoboa/admin/models.py
	modoboa/admin/templatetags/admin_extras.py
	modoboa/admin/views.py
	modoboa/core/app_settings.py
	modoboa/extensions/admin/forms.py
	modoboa/extensions/admin/tests.py
	modoboa/extensions/amavis/views.py
	modoboa/extensions/limits/tests.py
	modoboa/extensions/postfix_autoreply/models.py
	modoboa/extensions/sievefilters/views.py
	modoboa/extensions/webmail/fetch_parser.py
	modoboa/extensions/webmail/imaputils.py
	modoboa/extensions/webmail/lib.py
	modoboa/extensions/webmail/templatetags/webextras.py
	modoboa/extensions/webmail/views.py
Fixing admin unit tests.
Merge branch 'master' into refactoring
Various changes. Migration to the new layout is now ok.
PEP8 compliance and cleanup.
Merge branch 'master' into refactoring