Dev Stream Fun

1) Layout changes in the EntityShotBase class to support using the
"UNDEAD" trait of Entities, allowing me to not hard-code undead checks
in several items; The Exorcism shot required a restructure as a result.
2) Stalker potion was supposed to have invisibility, which it now does.
3) Removed unnecessary call from the Destruction Catalyst for creative
mode.
4) Handgun now has a level-based recoil effect, prompted by a server
packet to the client telling it to pitch the camera up.
5) Substantially improved MercyCross undead and base damage, now uses
previously mentioned undead check.
6) Fixed a Wraith's Eye NPE in the tooltip.
7) Added our first packet handler, a very simple packet, and our mod's
message class.
8) Lightly modified the lang file to correct some out-of-place
punctuation.