Now it just downloads to the user desktop payloads received in packages
with type kdeconnect.filetransfer.
Added the package type define.
Created an an auxiliar QFile-like class with a small needed modification.
Added a commented test in the filetransfer plugin code (to be moved).
Now protocol version is only sent once (in the identity package)
Removed "isEncrypted" bit, using type "kdeconnect.encrypted" instead.
NetworkPackage's decrypt and unserialize return false when find problems
Updated tests.
