Added currency formatter

Added RP:CC(value) to format numbers into nice strings for display.
Changed all money dollar signs to use RP:CC instead. Fixed syntax error
in sh_weapons. Moved more stuff to hooks instead of gamemode overrides.
Added 'guitest' to rp_cash so it can be quickly worked on with
autorefresh (This is temporary). Changed cash to use floats instead of
integers. Moved car dealer spawn-menu into sh_teams.