Add Beatroot code by Simon Dixon for beat detection in MIDI files

1. Passing of objects by values into functions
   were replaced by passing them by reference, where it is worth it.
2. Code style was reformatted according to the MuseScore style

Reformat Beatroot code style
Fix fillBeats function (Beatroot): no interpolation between 1st and 2nd beats
Make the scope of local variable more narrow (Beatroot)
Integrate beat detection algorithm into MIDI import
Collect MIDI chords using time in seconds (instead of ticks)
Human MIDI import: cleanup rests
Add staccato to some human performed notes
Extract bar division analysis into separate function