[Collection] Contributions from Xinxiang

[xgao28]

Here are the pull requests in which I implemented some of the code of this project:

• [+] Added implementation of UserJoinUseCaseTest. #114
• [+] Added javadoc for userjoin use case. #63
• [+] Implemented user_join in usecases and UserJoinUpdatable in interface_adapters. #40
• Added github usernames of group members. #12

Here are the issues that I closed or contributed by the pull requests:

• [Documentation] Javadoc for UserJoinUseCase @xgao28 #55 in [Improvement 3] Adding Javadoc everywhere #44
• [Feature 10] UserJoinUseCase @xgao28 #30 in [Feature 3] Implement Use Cases in our CRC Model. #7
• [Feature 1] README and Wiki #3

Here are the issues and discussions that I commented:

• Linking all ViewModels to share the Updatable interface #37
• [*] Update interface and abstract class viewmodel #38

Here are the pull requests that I reviewed:

• [*] Revamped MySQLDatabaseGateway and other major modifications to use cases #76
• [+] Modifications on MySQLDatabaseGateway & added a SQL Script #62
• [+] Add deleteEntry Usecase #39
• implment a userfactory, Iuser interface, 1.0 #19
• [+] Add some initial implementations of entities. #15
• Updated README.md #5