[Feature request] Note groups

[RowanDDR]

Add the ability to mark, name, select, copy, and paste groups of notes within patterns. It could be a useful way to manage and visualise the chunks of repetitive notes/beats which repeat within patterns. It might look something like this (see below) or be implemented in an alternative way.

This feature request expands upon https://github.com/bazzinotti/snestracker/issues/26.

[bazz1tv]

(just pasting this from my private notes) An easy way to start mocking up Cut and Paste selections is by adding functionality for highlighting rows and columns while the Shift Key is selected. This can lay the foundation for later mouse selection code to use.