fix OAuthToken::clear and add test
add OAtuhToken::app property

all required fields for an OAuth token are implemented now
prepare management of OAuth tokens from Manager

todo: implement adding/deleting scopes by updating token through API
removing unused NetworkPrivate

should have done that long ago
fixing some bugs in OAuthToken implementation
update Manager API

* changed signature of some methods
add INetwork::patch
implement Network::patch

* improvements of HTTP HEADER debug output
adjust Manager tests to recent changes
improve Manager::updateThing

+ add Thing::changesToString() to only build request payload from
  changed properties; therefore also add caching of last json response
* using recently added PATCH method for updating instead of POST
for now completely disable UpdateUser test

updating the authenticated user will not work with current functionality
of the UpdateThing procedure.

todo: add special handling for updating data of authenticated user