Communities: initial release

* Introduces communities module

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

Conflicts:
	invenio/legacy/websearch/templates.py
login: fix permission issue for guest user

* Fixes a permission issue where a guest user did not have a list of
  permitted restricted collections calculated, causing issue with
  e.g. facets when viewing restricted collections (e.g. restricted to
  role anyuser).