Upload refactoring

When uploading a program, and something goes wrong on the web, a JSON object with statusCode and message is returned.
sample logcat output when uploading a program with incompatible xml version:
03-10 19:09:07.324: V/ConnectionWrapper(7683): {"statusCode":518,"answer":"Project contains old Catrobat language!","preHeaderMessages":""}

But we did not check the statusCode, and got "Upload successful" even when the program was not stored on the web.

This is just a quickfix - we should give meaningful errormessages; currently the same toast is displayed no matter what went wrong on the server.

successful testrun: http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/386/
(japanese test was removed temporarily because it did not work since change to FTP upload - but test was always green, because we didn't check the statusCode :D)