Cleanup

Clean up some of the code. Remove unused imports. Remove dangling instance variables leftover from refactors. Add some todos. Move ContactsAsync callback interface from separate file to nested in the class.

Most noticeable change is I rearranged the package structure. The original structure was getting too messy with all the new files so I organized into packages based on messages, friends, session, and music. Still might not be the best way to organize them, but something needed to be done. Feel free to organize further.

Touched a lot of files, but didn't really change much code. I tested all the functionality and everything seems good.