In mapmos, removed the requirement that all four lat/lon extents be entered by...

In mapmos, removed the requirement that all four lat/lon extents be entered by the user. The user can now enter either min/max lat or min/max lon. The other pair will come from the input cube. If the input cube is missing the pair, an error will be thrown telling the user that they have to enter them. Fixes #1550.

git-svn-id: http://subversion.wr.usgs.gov/repos/prog/isis3/trunk@5765 41f8697f-d340-4b68-9986-7bafba869bb8