Added MIDI clock and reverse play

Today I have added the internal MIDI clock and reverse play to the sequencer.

So it is now possible to play MIDI instruments without need of an external clock from a computer or clock generator!

Reverse play is the third play mode of the sequencer. As the name says, it plays the notes in opposite order than forward. 😉 Currently, there are the modes forward, reverse (or backward) and random play. There will be ping-pong play at soon, which is a combination of forward and reverse play.

Next steps are to integrate BPM control and MASTER/SLAVE switch in the menu, which will hopefully not overstrain me. 😀