Add ALSA-based volume control and test logic#8

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WasabiFan wants to merge 7 commits intoev3dev:ev3dev-jessiefrom

WasabiFan:add-audio-controls

Commits on Jun 21, 2016

Commits on Jun 24, 2016

Clean up sound code based on review feedback
WasabiFan
committed

Commits on Jun 25, 2016

Format audio code to follow spacing style conventions
WasabiFan
committed

Commits on Jun 26, 2016

Only show sound mixer index when nonzero
WasabiFan
committed

Commits on Jul 7, 2016

More clean-up of audio code
WasabiFan
committed