SideOnly on client only methods in gates

Problem: When loading a world that has gates, the server will crash with this exception:
http://paste.cisien.com/f/33730518.txt

Solution: add @SideOnly(Side.CLIENT) to the methods that deal with IIcon, since they are client-side only.

Tested item pipes with gates pulling items from a chest in single player, and in multi-player
Merge pull request #1459 from Cisien/patch-2

SideOnly on client only methods in gates