Func nav blocker

It's a brush entity that can block areas touching it so that bots will not attempt to go somewhere.

Keyvalues

 * {|class=tbl

!Value!!!!!!
 * -1
 * colspan="3"|Everyone
 * 2||Red||Survivors||Terrorists
 * 3||Blue||Infected||CTs
 * }
 * 3||Blue||Infected||CTs
 * }
 * }