Added static RNGseed control

 - rngseed CCMD, with three methods. Using method "get" allows you to view the current rngseed, "set <value>" allows you to set a static rngseed for the next game, and "clear" unsets the static rngseed.
 - "-rngseed <value>" command line arg sets a static rngseed. This allows for netgames or recordings to also use the set rngseed.