Buffer for previously pressed notes

again a feature from fls. If you dont know their 'mozart-buffer' this is how it works.
All note-keypres are 'recorded' to a rolling buffer, meaning that if we say the buffer is (array) 0..49 ~50 key-presses, then 1. keypress goes in 0. slot, but also the 50th. will end in slot 0, and so on -Eg the last 50 user keypresses are always _kept_ in this buffer.
The idea is that if you jam and suddently you hear somthing thats as great as Mozart, then you wont have to 're-do it', (and everyone knows how utterly impossible that is...) Instead you just open a piano-roll, and choose a menu-option 'Dump keybuffer to piano-rioll'
Hey presto, theres your epic series of Mozart-genious key-strokes, kept for prestarity and your own wealth... (ya right) - No -its a neat little feature, and it shouldent be too difficult to implement -or?

The issue names no files or tests. Start by locating note-keypress handling and the piano-roll UI/menu; the feature is done when the latest 50 keypresses are retained in a rolling buffer and can be dumped into the piano roll.

Written by the indexing model from the issue text.