This provides a nicer alternative to zoom scrolling.

This makes them work much nicer than the old timer-based
implementation.

Use the new long press delay factor to make the zoom scrolling
less easy to trigger accidentally.

Add a way to set a delay factor that can be used
to make the long press more or less sensitive.
Keep this private for now.

Allow dragging the various icon sizes as images.

Use a custom tree model and enable dragging from the icon view.
Currently, we just support dropping the icon name as text.

We want to get away from double-clicks everywhere.

We don't need the selection here.