Fix for Mantis 3064 from MageKing17: Adds more functionality to colors.tbl. 
* "#Start Colors" is now optional; no more need for a blank section at the start of a colors.tbl just to define some team colors.
* "#Interface Colors" section added for redefining various colors used by the interface.
* "#Color Tags" section added for redefining or adding your own text color tags.
* "#Default Text Color" section for choosing what color tag is the baseline default for various different screens.
* And the big one, support for *-clr.tbm modular table files.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@10926 387891d4-d844-0410-90c0-e4c51a9137d3