Various improvements

Changed spawned_shipment and spawned_weapon to use 'cost' instead of
'price'. Fixed the error in spawned_weapon when the player did not have
enough cash. Improved HUD to have a flatter and cleaner design, also now
shows salary - which fixes #26. Merged cl_localchat and sv_localchat
into sh_localchat. Added RP:FormatTime(t). Renamed sv_customname to
sh_customname to fix an issue where nicknames would not work clientside.
Fixed nicknames not unsetting properly. Added a menu system to teams,
such as the gun dealer - simply call ply:ShowMenu() on either server or
client, will return true if a menu opened. Modified gun dealer shop to
use menu system. Added shared RP.SalaryTime for display on client (HUD).
Added utility functions ply:GetTeam() and ply:GetTeamValue() and changed
things to use them instead of RP.Team[ply:Team()] and
RP.Team[ply:Team()].value respectively. Removed small blast damage from
walljumps on in the parkour script. F3 now triggers the menu system.
Renamed !shop to !menu. Changed !nick to !rpname. Attempted to fix
replicated convars (#29), but may be an issue with GMod itself
(Facepunch/garrysmod-requests#1234).