hack to avoid video thumbnailing in device mode
Add api for chaning scrollbar color + lighter default
Adds new RutIconButton widget

This adds a new button widget that lets you specify specific icons to
use for the different states; normal, hover, active and disabled. A
label can also be specified and you can specify whether the label should
be above, below or to the side of the icon.
Create asset selector buttons
Use icons for connect buttons
bit: queue redraw when setting child
fix: switch to connect button icon
for simple sizables return natural size of 0

This changes rut_simple_sizable_get_preferred_width/height to return 0
for the natural size instead of returning the current size.
Add more asset selector icons
Don't use a split view for the assets panel
shrink the light model
simplify split view, not allowing interactive dragging for now
Add support for resetting the view by pressing 0
Hide and show light when entering/leaving play mode
give asset selectors white labels
center the labels for the asset selectors
add missing asset selector icons
add missing connect icon asset