DVB: Add context menu to the navigation dialog.

Use std::vector to store channel in order to get better sort abilities.
DVB: Use proper media types.

Resolves ugly audio pops and cracks for EAC3.
DVB: Don't abort tuning when tuner refuse to set bandwidth.

Some tuners doesn't support setting bandwidth value. See related ticket
for more information.

Fixes #4436
DVB: Don't clear the channel list on saving new scan result.

Fixes #3666
DVB: Update event information on separate thread.

This change improves channel switching speed.

Fixes #2953
DVB: Open through Graph thread.
Navigation dialog: Various cosmetics.

Reduce the visibility of member variables.