AVWriter: update sample format list depending on the audio codec

* All the same behavior as pixel formats:
     * By default the list contains all sample formats supported by all
audio codecs.
     * The list is not correctly updated in Nuke (same problem in the
previous version of the plugin with the pixel formats).
     * Get all sample formats if the list is empty with the audio codec
indicated.
AVWriter: refactoring

* Rename updatePixelFormat to updatePixelFormats.
* Rename updateSampleFormat to updateSampleFormats.
AVWriter: refactoring

* Rename _paramVideoCodecCustom to _paramVideoDetailCustom.
* Rename _paramAudioCodecCustom to _paramAudioDetailCustom.
AVWriterFactory: set a default value to audio sample format
AVWriterFactory: refactoring

Rename audioCodecSampleFmt to audioSampleFmtParam.
AVReader: fix name of OFX params

Concern only child of OFX Group.
AudioVideo SConscript: no dependencies to FFMPEG

Update SConscript: remove dependencies to FFMPEG libs, and keep the
dependency to avTranscoder.
AVWriter: fix add dummy audio stream

Add an audio stream to the Transcoder when the user wants a dummy stream
with an existing and specific audio preset.
AVWriter: refactoring

Prefer an empty string when the presetName need to be empty.
AVWriter: fix output file when transcode video and audio

* The problem was: when try to read the output, which contains video and
audio streams, raise the error "Context scratch buffers could not be
allocated due to unknown size.".
* The fix: add the video stream to the output file before any audio
streams.
AVWriter: custom audio profile - refactoring

Create the custom audio profile only once, enven if the user wants
several audio streams.
AVWriter: rename - refactoring

* Rename audioStreamIdParam to audioStreamIndexParam.
* Change the label of the OFX param ("id" to "index").
* Change the name of the OFX param ("id" to "index").
AVWriter: fit to new avTranscoder API

* getPixelFormats is static.
* getSampleFormats is static.
AVWriter: remove check pixel format

If a wrong pixel format is set, avTranscoder raises an exception when
open video encoder. Not necessary to check the video profile.
AVWriter: remove check sample format

If a wrong sample format is set, avTranscoder raises an exception when
open audio encoder. Not necessary to check the audio profile.
AVWriter: fix pixel format when use custom video profile

Get the pixel format from the OFX param if the user wants a custom
profile, or directly from an existing profile if specified.
AVWriterProcess: add setup

During setup:
     * get image to encode.
     * get image rgb.
AVWriterProcess: update comments
AVWriter: use also transcoder to encode video

* In AVWriter, the instance of Transcoder:
     * transcode audio (like before).
     * encode the video stream.
* To encode the video stream: create a dummy video, add it to a
streamTranscoder in the transcoder, and set the frame of the dummy each
time in the AVWriterProcess.
* Thank to that, we don't need an OutputVideo, a ColorTransform, and
some intermediate Images: all of this is manage in the Transcoder.
AVWriter: create dummy video - refactoring

* Rename customPreset to profile.
* Move some code in ensureVideoIsInit function, to avoid repeated the
same code in several cases (if, else...).