Cmsplugin-feedback

- Form submition sends `form_submited` signal
- Managers will be notified with email on `form_submited`
- Add `feedback_form_tag` block to `templates/cms/plugins/feedback.html` for better customization
- Drop `CMS_FEEDBACK_FORM_CSS_CLASS` and `CMS_FEEDBACK_FORM_FIELD_ID`
- Freeze test requirements and djando-mptt version to fix CI
- Translations update

Django 1.7 support

- Transifex integration https://www.transifex.com/projects/p/cmsplugin-feedback/resource/main/
- Translated for Russian, Arabic and Belarussian

- `title` was removed from plugin model, because this looks not as a part of a form, it more like content before a form. If you want to place a title, it is better to insert a text plugin right before feedback form and put a text you want with it.
- `submit` and `ok_message` was removed from plugin model, because it more about template, not about a model. And it is easier to localise a text in a template, but not a model field. Less configuration makes plugin simpler, but you still can translate a text or override template blocks.
- A minor JavaScript improvements.

First stable version