Display keyboard shortcuts on Alt press and in tooltips

Tooltips of some toolbar buttons already show the keyboard shortcut, but it would be nice if all of them did, especially the tool mode buttons.

In addition as a bonus, it would be Awesome if, when pressing e.g. Alt or something, that the keyboard shortcuts are momentarily displayed under all toolbar buttons. Sometimes you just need a quick refresher if you haven’t used it in a while.

Feature requests and bug reports in the forums will generally be ignored or forgotten. They belong at http://tracker.ardour.org/