Added property names to undo commands

[bjorn]

• Set Property 'foo'
• Add Property 'foo'
• Remove Property 'foo'

Currently I haven't touched "Rename Property" because I think it would get a little too verbose if we mentioned two names. However, the name does mention the full path of a property if it is nested, separated by dots.

Also addressed a old occurrence of 'Type' which should have been renamed to 'Class' in Tiled 1.9.