FOV based on longer window dimension

This fixes #1591.  We're imitating STK's FOV behavior, where the longer dimension of the window's width or height is used for the requested FOV (as opposed to FOV always being relative to the window height).  This keeps the FOV setting from growing unbounded on very short wide windows.

This branch currently breaks a pile of Camera unit tests, I suspect because the tests are making bad assumptions about the FOV.  @bagnell can you offer advice here?  This will need to be fixed before merge.

Also, we may want to consider making the default view(s) "further away" to accommodate typical widescreen monitors, which all effectively got a (sometimes large) reduction in FOV as a result of this branch.