Checkboxes / Tree Icons / Dialog Icons don't scale with font size

[apocalyptech]

Just what it says on the tin -- when scaling font sizes there's some stuff which doesn't scale up/down appropriately. Namely:

• Checkboxes
• Tree Icons (expand/collapse, lock, comment, folder open/close), exec, say
• Dialog Icons: warning/error/info/question
• Red question-mark icons
• Game Icons in file-dialog shortcuts (also the "stock" home/up/new-folder/etc icons)

This would affect radio buttons too, if we used any.

For checkboxes, we'd have to implement our own Checkbox-rendering function, which might not be a huge deal, but I don't really feel up to it at the moment. For the other icons, theoretically that shouldn't be too big of a deal, though we'd need to get some larger source versions for some of those.

Anyway, not gonna work on this in the forseeable future, but wanted to get it in here. This is related to #28, which I'm hoping to close out pretty soon now.