Make more GridMap keyboard bindings configurable

[tavurth]

Describe the project you are working on

A project which uses GridMap

Describe the problem or limitation you are having in your project

I use a non standard keyboard layout (Colemak)

The current default keys to rotate or move up and down layers are fairly difficult to work with.

My Mac does not have a delete key so if I want to delete a selection I must do it by clicking two times, there is no shortcut.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Add Editor level InputMappings which can be configured, this should solve the issue

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

Please see above

If this enhancement will not be used often, can it be worked around with a few lines of script?

This is frustrating because a workaround is an everyday procedure

Is there a reason why this should be core and not an add-on in the asset library?

Core GridMap