Minor UI bugs

[rycoll]

Report minor UI bugs here:

• when decorations spawn in, they don't spawn at mouse position (but move there from off screen). This is because of the difference between mouse position and world space. It would also be nice if the decoration sprite could go over the Decoration Panel (then that panel could stay open).
• it is often unclear which map tile you're clicking, because of weird colliders. This is actually a big problem! (a temporary fix has been made - see below)
• it's weirdly difficult to open the dropdown for selecting room materials. Also the builder payment slider.
• opening the Treasure Panel removes any construction decisions you have made (doesn't just make them invisible, actually undoes them).
• parts of rooms can be blocked from sight by walls (and undug tiles). Possible solution: change undug tiles back to being flat?
• scrolling menus often clip of the ends of the first/last items
• the yearly report text will probably need to be scrollable

[rycoll]

Mousing over a sprite now makes it slightly transparent. This isn't a good fix, but it does at least make it clear which sprite is being selected. A better fix should be made!