Custom menu and submenu width via option settings

Replace the static 200px width with additional "width"-options for contextmenu and submenu.
The default width is set to 200px in the defaultOptions.

Usage:
```
contexrmenu: {
  width: Number, 
  items: {
    "menu-item": {
       ...
      submenu: {
        width: Number
      }
   }
}
```
or omit width-option to use defaults.