Added 'add' and 'remove' members management with null or empty list
Merge branch 'sc-socialengine' of
https://github.com/smartcampuslab/smartcampus.socialservice.git into
sc-socialengine

Conflicts:
	src/main/java/eu/trentorise/smartcampus/social/managers/PermissionManager.java
Added the pagination management in the group controller (Limit object).
Tested the new features.