toggle button: Convert to css nodes

toggle button: Convert to css nodes

Convert GtkToggleButton and its subclasses to CSS nodes.
Keep the button element name for when we want to render
these button-like (but with .toggle, .check and .radio
style classes for differentiation).

When we want to render them with an indicator, use distinct
element names checkbutton and radiobutton, and add a subnode
for the indicator with name check or radio.