Corrected infinite loop error in removeParticipant
Added first addParticipant test
Fixed errors in MockUserService that appeared after Conversation update
Added another test to ConcreteConversationTest
Cleaned ConcreteConveration

ACE-88
Added tests for isValidUserName, other tests encompass all other methods

ACE-88
Merge pull request #44 from ualerts-org/refactorConcreteConversationTest_ACE-88

Refactor concrete conversation test ace 88