Grid updating when changing channel

* Adds updateGrid function that updates the grid and instrument highlights to match the data for the channel
* Initial changes for getting all channels to play simultaneously (doesn't work though)
* Bug: when entering a song, updated channel data isn't being loaded.
Fixes bug in which entering a song would not load song data properly

* Adds updateInstrument function that updates the currentInstrument var from sequences
* Deletes channel data in sequences before updating it in getFBSongDataWorker (firebaseGetSongData)
* Updates updateGrid to remove highlighting of an instrument if changing from another channel (otherwise, if entering song, no need to unhighlight)
* Changes playNotes to load channels based on sequences instead of Firebase since sequences is getting updated properly now
removing commented out/unnecessary code; one section left in - Firebase updates - unsure if these are needed, doesn't seem they are
Merge pull request #24 from artfoundry/grid-update

Grid update