Make flatpages Django 1.9 compatible

[ziima]

It's going to be tough. The solution recommended in https://code.djangoproject.com/ticket/26762, only works in Django >= 1.9.

It seems the only solution is to make settings dependent on Django version.

• [x] Rename flatpage table #112

[ziima]

We will probably have to rename the fuflatpage table outside of migrations.