Add keyboard control for sizing and moving, and a help button to explain how it works.

Author: dpvc

ts/a11y/explorer/KeyExplorer.ts

@@ -969,19 +969,6 @@ export class SpeechExplorer
           'font-size': '20px',
           margin: '.5em 0',
         },
-        'mjx-dialog kbd': {
-          display: 'inline-block',
-          padding: '3px 5px',
-          'font-size': '11px',
-          'line-height': '10px',
-          color: '#444d56',
-          'vertical-align': 'middle',
-          'background-color': '#fafbfc',
-          border: 'solid 1.5px #c6cbd1',
-          'border-bottom-color': '#959da5',
-          'border-radius': '3px',
-          'box-shadow': 'inset -.5px -1px 0 #959da5',
-        },
         'mjx-dialog ul': {
           'list-style-type': 'none',
         },