Added dynamical group authorization

Conflicts:
	main/squid/ChangeLog
do not skip empty groups when generating rules, they can be populated later
Added kerberos dynamic group authentication
Merge branch '3.5' into jacalvo/squid-group-auth

Conflicts:
	main/squid/ChangeLog
	main/squid/src/EBox/Squid/Model/AccessRules.pm
	main/squid/stubs/squid.conf.mas
Merge pull request #1513 from Zentyal/jacalvo/squid-group-auth

Jacalvo/squid group auth