Merge djangocms-common into aldryn-common

At: https://github.com/divio/djangocms-common/commit/588dd26abb33afb618d070454e8f773a09cf0d29

Cleanup is to follow, but we need to ensure a good
deprecation practice
Merge pull request #3 from aldryn/merge

Merge djangocms-common into aldryn-common (closes #2)