Add "inherited" properties to properties dialog/panel

[ghost]

Love the new properties panel. One thing that would be nice would be to have it show (in an un-editable way) any properties attached to the tile itself. For example, I use tile properties on images to set up some standard properties that apply to all instances of that object and then use per-instance properties for specifics. It would be nice, as a reference, if I could see those tile properties in the properties sheet. I wouldn't expect them to be editable (since they're not instance properties), but the reference of seeing them would be nice.

[bjorn]

I like this suggestion. Though there's a small difficulty in representing this differently from properties that are shared (or not shared) with other selected instances, when I ever get around to fixing #5.