Got basic reading of accelerometer, gyro, and keys working.

Signed-off-by: Chris Reed <flit@me.com>
First step in generating MIDI output.

- New SignalSource and MIDIGenerator classes.
- Created instances of source and generator classes owned by the app
  delegate.
- Added combo box for X accel generated MIDI CC number and supporting
  code in the app delegate.
- -availableDestinations returns both virtual and real destinations now.
- Setting accelerometer characteristics to shortest working period.
- KVO observer passes signal changes to SignalSource instances.
- Basic MIDI CC generation.

Signed-off-by: Chris Reed <flit@me.com>
Added inclination angle calculation.

- Signal sources now have units and can format their value as a string.
- Added Auto Connect checkbox and support for reconnecting after a
  connected device is disconnected.

Signed-off-by: Chris Reed <flit@me.com>