WIP: Homescreen grouping (v2)

Everything is in a group, dividers act as group separators.

Working (to a fashion):
- Rearranging groups
- Expanding/collapsing groups
- Creating new groups between groups
- Saving/restoring collapsed state
- Transitions

TODO:
- Editable group names
- General polish and optimisation (pending Gecko bugs)
I think that we could do:

```js
var type = this.gridView.items[checkIndex].detail.type;
if (type === ''placeholder'' || type === 'divider') {
  return;
}
```