Editor behavior: shift/drag selection + switch to left click

[fasterthanlime]

Here's what I had in mind before the jam deadline:

• Only select when "shift" is pressed
• Allow selecting multiple cells with "shift+drag"
• Change all the context menus to be triggered on left (normal) click instead of right click
• Change name editor to just toggle between option A and B when there's only two choices (example: for flippers - instead of showing a context menu with 2 options).

I think this would be more intuitive (except for the selection part, but that's advanced behavior anyway).