Represent note velocity as actual MIDI value instead of percentage

Currently the velocity is represented as a value between 0 and 200 in the PianoRoll and later translated to the standard 0-127 range for MIDI instruments. Most people are probably ok with this. However advanced users usually like to see what they are doing, so displaying the actual velocity value would really help.

This could be a disableable setting for those who prefer the current behavior, but if we move to this new approach completely, several other things would also become more simple and logical.
For example, this whole base-velocity nonsense could be completely trashed. (uh, that was harsh)
In the builtin non-midi synths 127 should correspond to what is 100% now, 0dB. No point of allowing more than that anyway.

There was a debate around handling velocity on MIDI import and export, this would also be solved instantly.

Start by tracing the PianoRoll velocity representation and the MIDI import/export paths, then inspect how base velocity is used by the builtin non-MIDI synths. The issue does not name files or tests, and completion would require resolving the proposed behavior and setting scope before defining what done means.

Written by the indexing model from the issue text.