Renamed MockUserService to ConcreteUserService

ACE-87
Removed unnecessary comments and beautified code

ACE-87
Created ConversationFactory interface and implementation
Implemented and corrected ConcreteChatService tests
Refactored ConcreteChatService to implement ConversationFactory
Formatted ConcreteConversationFactory and ConversationFactory
Added CreateParticipantTest file (incomplete)
ACE-87
Test ConcreteConversationFactory with ConcreteConversationFactoryTest

ACE-87
Use setUp() method for initializing context and userIdentity fields.

ACE-87
Use setUp() function in place of multiple identical instantiations in...
ConcreteChatServiceTest and ConcreteConversationFactoryTest

ACE-87
Satisfy ConcreteConversationFactoryTest.createConversationTest() by...
having the mocked ConversationFactory call its createConversation
method.

ACE-87
Remove duplicate mocked Conversation in...
ConcreteChatServiceTest.testJoinConversationWithConversation()

ACE-87
Merge pull request #46 from ualerts-org/finalImplementationOfUserService_ACE-87

Final implementation of user service ace 87