AVWriterPlugin: fit to new avTranscoder API

* Video: setProfile with a profile des and an image desc.
* Use const name of Profile.
can set a customProfile for dummy audio streams
AVReader: fix PAR

* Retrive Pixel Aspect Ratio of image depending on:
     * if the host supports PAR, return 1.
     * else if user wants a custom PAR, return the custom PAR.
     * else return the PAR of the video (get it from input file).
* ReaderFactory: declare the support of MultipleClipPARs
AVReader: refactoring vary on time

* Rather redefine an existing function than set the param in
getClipPreferences of the plugin.
AVReaderFactory: set range to the customSAR param

* Display range: 0 - 3
* Real range: 0 - 10
* Update hint of the param to indicate the maximum value.
AudioVideo: OFX group params are close by default

* Better visibility (there are a lot of OFX params in reader and
writer).
AudioVideo: refactoring

* Move struct CustomParams to common/util (will be used by the Reader
and the Writer).
AudioVideo: refactoring

* Move prefix (const strings) used for OFX params name to common/util
(will be used by the Reader and the Writer).
AVReaderFactory: set range of streamIndex param

* Display range: 0 - 16
* Real range: 0 - 100
* Update hint of the param to indicate the maximum value.
AVReader: refactoring ensureVideoIsOpen

* No need to have a parameter: get the filepath at the beginning of the
function.
AVReader: fix when select a non existing video stream

* Thow exception if the user wants a video stream which doesn't exist.
* Add _lastVideoStreamIndex to check if the user wants a new video
stream (same idea as _lastInputFilePath).
AVReader: add flag to get if video stream is initialized
AVReader: refactoring

* Add cleanInputFile function to clean all attributes about the video
stream.
AVReader: update range of VideoStreamIndex param...

...depending on the number of video streams in the inputFile.
* The user can't set an invalid video stream index with a host like
Nuke.
AVReader: fetch custom params

* Custom params of:
     * format
     * video
     * audio
     * metadata
* Warning: Only create OFX params and fetch them with the Factory ; no
impact with the render. To do this, we need to update avTranscoder
objects depending on this params.
AVReader: refactoring

* Rename _idVideoStream to _videoStreamId.
* Suppress unused includes.
AVReaderProcess: clean

* In the process, immediately return the View doesn't show a black
image.
AVReaderPlugin: suppress warning

* Avoid comparaisons between signed and unsigned numbers.
AVReaderProcess: add comment

For interlace.
AVWriterPlugin: check pixel format when create video stream

* The list of video pixel formats is not correctly display in some host
like Nuke: all the pixels format are accessible to the user. If the user
try to process with a wrong pixel format selected (according to the
video codec), throw exception.