Minor corrections
Removed unnecessary header inclusion from the the main video header
Implemented the internal VideoPlayer class

It will take care of playing the video and thus computing the current frame in an external thread.
Thus, it removes the need in the user code to update the video before drawing it
Internally, it solves one issue which is the inability to compute this frame in the draw() function since it is marked as const.
Later, both sf::Video and sf::VideoStream will use it internally.
Replaced status raw constants with an enumeration in VideoPlayer
Updated Video's internal implementation to make use of VideoPlayer

The need to call update() has been removed.
Upgraded VideoPlayer to play a queue of video buffer
Implemented VideoBuffer::loadFromFrames()
Implemented VideoStream
Implemented Movie
Implemented VideoRecorder
Updated CMake scripts to include and link against OpenCV
Implemented VideoBufferRecorder
Added video capture example
Updated video example to stream the movie sample (with sf::Movie)
Fixed indentation