Updated gitignore
Added requirements.
Made app runnable from includedd test app.
Updated to cms 3.

* Changed LinkExtension.link to cmsplugin_link.Link.
* Added schemamigration for it.
* Updated requirements
Removed base.html in the old location.
Flake8 cleanup
Updated requirements
Made extended link its own plugin to prevent issues with related names.
Removed unnecessary forms.py
Merge branch 'develop'
Released v0.2