Add piano roll pointers to core musical entities

[ricardomatias]

Musical entities (Scale, Chord, Key) should not have a closed range of musical notes. They should start somewhere in the piano roll and then be able to move.

Having a Cmaj starting at C3 (C3, E3, G3)

• Move N octaves Up/down
• Spread along N octaves, f.ex: 2 octaves -> C3, E3, G4
• Repeat at another octave