Implement PC Buttons and LEDs

[nathanlong85]

This will just be for sending PC messages initially.

• A MIDI channel should be decided on already, but if not, decide on it
• PC buttons will change patches or presets
• There should only be a single LED active at a time for the PC buttons.
• When a PC button is pressed, all CC button states should go LOW before sending the MIDI message to change preset. No CC MIDI messages should be sent when switching state.
• PC values should probably start at 1 (or 0?) and go in blocks of 5. Blocks will be implemented later with the StepUp and StepDown buttons
• The current PC value should be displayed on the LCD

[nathanlong85]

Here's some quick and dirty Ruby to calculate the number of banks and preset range per bank for a given number of PC buttons

PC_COUNT = 5

num_banks = 127.0/PC_COUNT
banks = (0..num_banks).to_a

banks.each do |bank|
  min = bank * PC_COUNT

  max = 
    if min == 127
      127
    else
      m = min + (PC_COUNT - 1)
      m > 127 ? 127 : m
    end

  puts "Bank #{bank}: #{min} - #{max}"

# (0...PC_COUNT).each do |preset_multiplier|
#     preset = preset_multiplier + (bank * PC_COUNT)
#     break if preset > 127
#
#     puts preset
#end
end