AVWriter: always get video encode params from video OFX params

* Need to manage flags and other exceptions of FFmpeg in setOption
function (common/util.cpp)
* Need to get this feature with format and audio parameters.
AudioVideo common: refactoring CustomParams class

* Store OFX parameters in a single vector: _paramOFX.
* Use dynamic_cast when it is necessary to get the value of the
parameter.
AVWriter: always get audio encode params from audio OFX params

* Need to manage flags and other exceptions of FFmpeg in setOption
function (common/util.cpp)
* Need to get this feature with format.
AVWriter: clean changedParam

* No need to show and enable OFX parameters when custom video / audio
presets changed.
AVWriter: always get format encode params from format OFX params
AVWriter: refactoring get custom profile functions

* Remove getCustomXXXProfile functions (for format, video and audio).
* Get format, video, and audio profile respectively in initOutput,
ensureVideoIsInit and initAudio.
AVWriter: update format depending on the output file extension

* In initOutput function, before getting the format profile, update
format OFX parameter depending on the output file extension.
AudioVideo: fit to new avTranscoder API

Update includes.
AudioVideo: scons - update avtranscoder lib name
AudioVideo: fit to AvTranscoder API

* Resume of AvTranscoder news:
     * remove OptionLoader
     * add util
     * add Context
     * profile constants defined in "constants" namespace"