Allow keyboard shortcuts to be scoped to a dom element

This gets rid of the need to enable/disable the keyboard handling
at various times.

Allows Ctrl-C to work as expected when selecting text in debug/info
sidebar.

Downside is shortcuts that apply to the workspace (select-all, copy
etc) now require the workspace to be focussed.

editor/js/ui/library.js

@@ -472,10 +472,8 @@ RED.library = (function() {
                     ],
                     open: function(e) {
                         $(this).parent().find(".ui-dialog-titlebar-close").hide();
-                        RED.keyboard.disable();
                     },
                     close: function(e) {
-                        RED.keyboard.enable();
                     }
                 });
             exportToLibraryDialog.children(".dialog-form").append($(