Bug 1024623 - [Vertical] Add collections to customization of vertical homescreen
Merge pull request #20531 from mcjimenez/bug1024623

Bug 1024623 - [Vertical] Add collections to customization of vertical homescreen
Bug 1022713 - Only render the necessary icons when dragging. r=kgrandon

Dragging an icon previously caused all icons from the first icon that needs
re-rendering to the end of the grid. This makes sure that only the icons
that are affected by the rearrangement are re-rendered.
Bug 1022713 - Add styles for when the grid is scrolling and for visible items. r=kgrandon