Adds ctrl/cmd+s shortcut to whole application with a noop default

closes #4516
- shortcut for ctrl/cmd+s on application level
- shortens a syntax for any route that is using 'save' method, shortcuts object doesn't have to be defined at all, only the save action.
Might be nice to do all the shortcut assignment in a consistent style, ala

```js
var ApplicationRoute,
    shortcuts = {};

shortcuts['esc'] = {action: 'closePopups', scope: 'all'};
shortcuts['enter'] = {action: 'confirmModal', scope: 'modal'};
shortcuts[ctrlOrCmd + '+s'] = {action: 'save', scope: 'all'};