Sequencer

Implementing song sequencer and improvement to the instrument class. Introducing the concept of tracks and sequencer.

Todo

[x] SongSequence - The resource that contains the data of the sequencer like tempo, list of tracks
[x] Sequencer - Sequencer plays SongSequences
[x] Tracks - A track is a set of notes playing in one instrument.
[x] Playing notes from the instrument class - Allows us to have different types of instrument - Synth style and Launchpad style