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)
tIndex + 1 is checkIndex
````js
if (this.gridView.items[checkIndex] === this.icon) {
```

up to you
```js
  ++checkIndex;
```