Add config option to set camera lens

Setting the camera lens causes the view to look "squished" on OSX and so the line was removed by #5, but apparently this causes issues on linux because it was reintroduced in c4b7eb98d8d5f6611c9240e256a07737c106e9ec. This commit adds a configuration variable to control whether the lens is set, so people on linux can set it to true (the default) and people on Mac can set it to false.