a toolbar in the map item properties panel
This moves the
- refresh preview
- set to map canvas extent
- view extent in map canvas
buttons from being oversized push buttons within the item properties
panel up to a new toolbar at the top of this panel. Apart from looking
better, it means these important actions are always visible regardless
of the scroll position of the item properties panel itself.
Additionally, it makes it possible to add MORE actions here without
overloading the UI (e.g. "set canvas extent to item extent")
TODO: better icons
