Support for interactive controls

[denis-stepanov]

When running from command line, it would be useful to listen to user keystrokes in order to react on the following input:

• (space) mute or unmute - useful when the tool goes into a wrong mode;
• m - explicitly mute, or do nothing if muted;
• M (shift-m) - explicitly unmute, or do nothing if unmuted;
• q - gracefully exit - because currently exiting is hard.

[denis-stepanov]

Also:

• c- decrease confidence threshold by 1%
• C (shift-c) - increase confidence threshold by 1%

[denis-stepanov]

As frequently happens, many more things had to be done. It turned out that Python has no-builtin capability to read un-buffered input. After experimentation a new dependency sshkeyboard has been added. The final list of commands:

h     - help
t     - emulate a hit
a     - toggle TV 'in action' status
space - toggle mute
m / M - mute / unmute
v / V - volume lower / raise
i / I - interval decrease / increase
c / C - confidence decrease / increase
q     - quit

n / N (changing thread number on the fly) was too laborious to implement in scope of this ticket; it was forked into a separate issue #68.

Other notable changes on the way:

• introduced new option -A which would allow starting TV "in action" (useful when TV happens to be muted upon AdVent start-up);
• added concept of uni-/bi-directional TV controls;
• refactored TV control API. The change is functionally compatible (i.e., represents extension of functionality), but signatures of methods of TVControl class have changed; so all TV controls had to be adapted;
• volume input parameter for PulseAudio was constrained to percentage of volume. Previously nearly any valid parameter accepted by pactl was possible, but it was hard to maintain that functionality in line with other controllers.