DVB Header information for video streams

Added header information from PMT tables for MPEG-2 and H.264 Streams. The switching channel approach had to be reviewed as well.
Minimized the number of windows size changes each time a channel is switched

Signed-off-by: xpc1000 <xavier_portell@hotmail.com>
Merge pull request #51 from xpc1000/master

DVB: Use the header information to improve the channel switching process.
Update Changelog.
DVB: Get the statistics info from the correct BDA nodes.

Retrieve the signal statistics, i.e. strength and present-flag, from the RF tuner node and quality and lock-flag from the demodulator node to ensure best compatibility with all BDA drivers.

Thanks to robert_s.

This commit fixes #3019.
DVB: Add "No subtitles" to the stream selection menu.
Subtitles are disabled by default now.