Fix crashing of muffin when monitor layouts or primary monitor is changed

[mtwebster]

Solves:
#810
#329
#302
#553
#968

Remaining issues:

Muffin: Should detect when a monitor is add/removed - currently it does not

There is a related pull in linuxmint/nemo#16

[mtwebster]

I'm happy with this request now - fixes a lot of problems. The remaining ones I think aren't cinnamon-related and can be addressed later.

[mtwebster]

@AlbertJP when you get a chance, can you verify the behavior of your computer in expo view without any of these patches? Even on plain master, on my machine, I still get extra-wide expo thumbnails.

[mtwebster]

I also want to point out that if you use a 2nd monitor as the secondary, and to the RIGHT of the primary, some of these issues weren't apparent. It's only when you try to rearrange, or make a different one primary, that alot of this bad behavior occurred.