applied updates from old issues/1894-stream-hierarchy branch
ref #1894 [code refactoring, introduced session, media streams]

- some methods are marked deprecated
- changed library API interface
- introduced session class
- introduced media stream class
ref #1894 [implemented adding local streams to the session]
ref #1894 [added remote sessions' observers]

- added remote session observers for monitoring updates in remote
sessions
- improved stability - proper shut down of media threads
- added audio threads
ref #1894 [added checks for valid callback in service channel]
ref #1894 [added functionality to face wrapper for pending interest removal]
ref #1894 [remove pending interests upon stopping service channel]
ref #1894 [changed library interface for remote observers]
ref #1894 [upgraded consumer classes, deprecated consumer-channel class]
ref #1894 [implemented consumer streams]

- updated library interfaces for adding remote video streams
ref #1894 [fixed serious crash on app termination]
ref #1894 [moved all name components used in a separate public header]
ref #1894 [fixed bug with restarting consumers]
ref #1894 [added check for already running streams in addRemoteStream library call]
ref #1894

- introduced Consumer observer interface - for receiving callbacks from
consumer of remote media streams
- implemented thread switching “on-the-fly” with dumb strategy: upon
changing media thread, pipeliner changes name component in it’s
interests’ names which corresponds to the new thread, also key frames
counter is incremented by 1 which means pipeliner is forced to request
next key frame from new thread. however, no buffer flushing is
implemented.
- updated library interface
[bugfixes] fixed assertion fail on line 612 and spelling
[untracked] introduced error codes
[untracked] added python module with helpers for parsing ndnrtc log files
[bugfixes] fixed thread-locking bug for face wrapper

- implemented RAII for accessing a face in the face wrapper class
[untracked] added session initialization method