Communities: initial release

* Introduces communities module

Signed-off-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
Co-authored-by: Grzegorz Szpura <grzegorz.szpura@cern.ch>
communities:

* Renaming
* config
* absolute import
* remove validator
* remove templates/__init__
More communities
Community: various fixes

* Fixes buttons for provisional collections
* Adds receivers file
* Adds file with tasks for celery
* Removes hardcoded conf from views.py, other cleaning tasks
Communities: some tests introduced

Tests for views and models