Updated pom xml with jackson dependencies
Fixed Jackson JsonHttpMessageConverter:
- set up supported media types
Added FriendCommandsController:
- Method that provide ability to set subscription on user. Similar to "add to friend action"
- Method that provide ability to unset subscription on user. Similar to "remove from friends action"
Added PostCommandsController:
- add tweet
- delete tweet
Added UserPostController:
- delete user

Changed implementation of create methods in service, repository packages for Post and Users. Now methods return newly created ID ( Integer) in case of success and 0 in case of fail