#JC-1428 Unit testes wete simplified.
#JC-1428 Refactotirng after code review.
#JC-1428 Logic of checking whether notifications are enabled or not
moved to MailService.
Merge branch 'master.senleft'

Conflicts:
	jcommune-service/src/main/java/org/jtalks/jcommune/service/nontransactional/UserMentionService.java
	jcommune-service/src/main/java/org/jtalks/jcommune/service/transactional/TransactionalTopicModificationService.java
	jcommune-service/src/test/java/org/jtalks/jcommune/service/nontransactional/UserMentionServiceTest.java