Dropped Django 1.4 support officially.

The templates and translated-fields code doesn't support it already,
so make this official now.
Fixed running Django 1.7 migrations in Python 3
Add Django 1.7 migrations to the testapp
Fix the '/path/to/page/@admin' redirect tests for Django 1.7
Bump version to 0.9b3 to support new versions of dependencies

NOTE: this release requires special attention when upgrading.
The `HtmlPage` models have changed, moving the
`meta_keywords`/`meta_description` fields.
See the `CHANGES.rst` for details how to upgrade.