Various board improvements

Removed unneeded materials

Added a TODO note to the camera manager

Added random rotation of empty systems. For variety, since there will
often be many on the map. Also have a
system in place for randomizing
which of the two varieties is used, but
I haven't added the other
texture yet.

Fixed board display issue and updated texture load

Fixed issue where
hexes were in a position mirrored top/bottom to where
they should have
been.
Updated texture loader to use system names, and only resort to
placeholder textures when a file isn't found.