Editor: Expose the clickable property of room objects

Allows the .Clickable property of objects to be toggled via the editor's
Properties UI. This functionality was already built into room objects,
I'm just exposing it. This commit also corrects some spelling errors.
Merge pull request #167 from gurok/331_expose_clickable

Bug Tracker: Add "Clickable" option to Objects in Editor.
Merged upstream pull request #167