Added a new tab

Added a new creative menu tab called "Evocraft Materials": This is for
objects like ingots, metal plates, metal tubes, etc. Essentially, highly
used materials that are used in practically everything.
Added a new tab and changed a graphic

Added a new creative tab called "Evocraft Weapons" for weapons in future
updates (and ammunition).
Also changed the "Evocraft Core" tab's picture to the Mech Platform Base
block.