Add Roman numeral (harmonic annotation) mode.

[yrammos]

This would be a major new feature.

A "Roman numerals" mode would enable the app to replace MuseScore in the DCML harmonic annotation workflow.

This harmony mode would involve a different set of keyboard shortcuts. Any reductive annotations would also be either disabled or invisible.

Functionality to skip forwards and backwards in metric space is already implemented in the code. Still missing is a correctly placed, "smart" text box for entering and correctly rendering Roman numerals, including any subscripts or subscripts.