"Invert Selection" depends on setSelectionMode (not set)

[m-7761]

I don't know, maybe it should be used in combination with the selection tools? Anyway, the selection tools don't call setSelectionMode automatically. I'm going to have them do so in the activate method and see if it sticks?

It looks safe except for selectFreeVertices that "Select Free Vertices" uses. I was just going to work on that anyway! Like today. I'm looking at this stuff as I compose this Issue. Sorry.

As an aside selectFreeVertices doesn't really work properly. I had a model today with free vertices that it couldn't select. I'm going to remove "m_free" (I think) since I have a member that is a list of faces belonging to each vertex, that can just be checked to see if it's empty or not. And remove setSelectionMode at the same time.

[m-7761]

For the record, selectFreeVertices doesn't have a reason for calling setSelectionMode as it stands. I think it should not be exposed as a public API and should default to face mode. It should only be available to the Tool system.