Enhance display of note names

[mmower]

Unless you turn on "Show Notes" it is very difficult to work out which note is associated with each hex.

We should investigate displaying the note name in the inspector and maybe also on the layer itself (e.g. a display in the corner that updates as the mouse moves over the layer).

[mmower]

I've implemented a simple display of the last selected hex but a hover approach would be more useful.