simplify menus shortcuts editing

[pmp-p]

by adding the possibility to edit ( maybe with right mouse click ) actions directly from drop down menus or at least show a message box with the override name of targeted action and a widget that can display a user entered shortcut to help filling keymap.json.

i found that https://github.com/redmunds/brackets-display-shortcuts that may be related

[abose]

Thanks for the suggestion. Related to #147 please track progress in that issue.