paper-submenu - option to disable animations

[TomasAgoston]

We would like to see a 'noAnimation' (or 'noAnimations') property for the paper-submenu that would disable animation on the iron-collapse (set its 'noAnimation' property).

This would be consistent with 'paper-menu-button' and 'paper-dropdown-menu' noAnimations properties.

Animations are resource hungry, bringing our application to the knees on mobile devices.