move DAO exceptions to own package
change Track download to use TrackDAO. also now downloading as gzip
remove loopj Async HTTP client. everything provided thru DAOs now.
change Track uploading to TrackDAO
let DAOs extend BaseRemoteDAO to leverage from gzip etc.
move User.java to .model package
add getUser implementation for RemoteUserDAO; some DAO improvements
use RemoteUserDAO for Login- and RegisterFragment
some DAO exception refactoring (reflect hierarchiy and semantics better)