This fixes the following (at least):
- encoder is instanciated first, which is better because there are devices that can't instanciate both hardware encoder and decoder at the same time, the second one be forcibly a software fallback
- encoder is reset() upon device rotation, because some encoders don't accept a reconfiguration otherwise
- decoder is reset() only if flush() doesn't work
- fixes the lack of use of 'offset' parameter in MediaBufferInfo provided by the encoder - could lead in outputing corrupted h264 bitstream.
- use getInputBuffer() and getOutputBuffer() instead of deprecated getInputBuffers() and getOutputBuffers()

Lots of cleanups and clarification, and new debug logs.