Use VideoProperties::getProfile() method.

This check is already done by av_get_profile_name method.

* Use Frame class instead (allocation/free is managed by the class).

Use Frame::getEncodedSize() method.

* Use VideoProperties::getGopSize() instead.
* Add doc to this method.

* To get the level of analysis asked inside member methods.
* Will be used in the next commit.

* AVCodecContext->gop_size is unused when decode according to the ffmpeg
documentation:
https://ffmpeg.org/doxygen/2.8/structAVCodecContext.html#a9b6b3f1fcbdcc2ad9f4dbb4370496e38
* So compute this info when analyseGopStructure, and store it inside the
VideoProperties class.
* Because the gop size could be used inside getBitRate() method, throw a
runtime exception before using it.

* Before: picture type, is key frame
* After: picture type, encoded frame size in bytes
* Note: "is key frame" info can be found using the picture type (I
frame).
* Updated SWIG interface.

…perties

To improve readability.

All properties have the same value if not found.

…t gop

All properties have the same value if not found.

Like other getter to properties.

Need to analyse first GOP to compute bitrate and get gop size of output.