util: fix getFormats Long / Short Names

Skip the first one which was an undefined codec in the enum list.
Transcoder: add method add( StreamTranscoder& stream )

* Manage memory of StreamTranscoder by spliting streams into 2 vectors.
* Add pyTest "testTranscoderAdd" to test if we correctly manage memory.
IInputEssence: add documentation for setFrame
Transcoder: refactore - get only one addTranscodeStream private method
Transcoder: refactore addDummyStream

Get only one instruction "new".