AVReader: refactoring

* Clean unused includes.
* Rename _imageToEncode to _imageToDecode.
* Update message when throw exception in ensureVideoIsOpen function.
AVWriterPlugin: manage Options with avTranscoder

* Update disableAVOptionsForCodecOrFormat function (use OptionLoader
object).
AVWriter Plugin & Process: encode video with avTranscoder

* AVWriterPlugin:
     * stop using a LibAVVideoWriter instance to encode video.
     * define ensureWriterIsInit function: use OutputFile and
OutputStreamVideo from avTranscoder to get the video stream.
     * store more data in AVProcessParams: formatName, videoCodecName,
audioCodecName.
     * refactoring: rename PixelFormat to AVPixelFormat (fit to new
naming convention in ffmpeg).
* AVWriterProcess:
     * update multiThreadProcessImages: use ColorTransform and Image
from avTranscoder to encode video.
* Warning:
     * Problem when encode video with pixel format yuv420: odd color of
encoded image...