Move "Browse Web Fonts..." stub into the code hints menu

Provide key board accessibility and fix layout issues

fixes issues: 
- https://github.com/adobe/brackets-edge-web-fonts/issues/77
- https://github.com/adobe/brackets-edge-web-fonts/issues/36
- https://github.com/adobe/brackets-edge-web-fonts/issues/35
- https://github.com/adobe/brackets-edge-web-fonts/issues/27
- https://github.com/adobe/brackets-edge-web-fonts/issues/26