Updated wagtail to 0.7 beta
Fixed reference to deleted wagtail module
Make sure six>=1.7 is installed
Added missing migration for focal_point_key change
Fix rcarendition_focal_point_key migration to set default='' and remove duplicate renditions
Use Wagtail 0.7 from pypi
Enabled wagtailsites module
Merge branch 'wagtail-0.7' into develop