support unregistering typewriter button updaters
react to octave change in typewriter
support octave selection in typewriter manager
implement octave selector
make get_closest_keymap_pitch work with low pitches
add a getter for selected octave
use toggle buttons for octave selection
add leds to octave buttons
implement get_pitches_by_octave
update octave button leds
Merge pull request #85 from cyberixae/implement_octave_selector

Implement octave selector