Use current_page instead of request for is_current

Since we already have the 'current page' object, we can compare it
against ourself to find if we are current.
rm unused import
Use content_model not the base Page in PageAdmin

When calling methods on a page, they should be called on the subclass,
not the base Page. This allows page types to override them.
The usage of reversion can now be disabled for DisplayableAdmin
Merge remote-tracking branch 'stephenmcd/master'
Syntax warning removed
Syntax warning removed
Merge
Merge
Merge
Update admin menu docs to mention labels for regaulr models.
Merge
pep8 fix
Added new site to README.
Merge
Merge
Change new reversion setting to be opt-in instead of opt-out.
Merge branch 'master' into develop

Conflicts:
	mezzanine/pages/models.py