Completely restructure message transfer between indico and app in order
to allow implementation of OAuth requests:
- HTTP communication outsourced in an intermediate layer, and classes
providing functionality for signing messages have to implement the
interface defining the intermediate layer.
- Indico API Connector only builds request URL, puts get/post parameters
and, calls the HTTP request from the intermediate layer and processes
the answer from the server

The current code is tested with the apikey and secret method, however a
class implementing the OAuth protocoll is also prepared.
Remove debug statement and add file which was forgotten before
Add license statement, and for some classes further documentation
Cut down license file to pure license declaration
Fix also post request using oauth
Merge branch 'OAUTH'

Conflicts:
	src/indico/checkin/core/gui/IndicoCheckinAppMainGui.java
	(resolved manually)
Authentification data for CERN indico