Fix Iron Mass giving Skeletons Triple Damage in Offhand

[Blitz54]

Fixes #3951.

Description of the problem being solved:

As far as I know there was no way to search for Item names in Modparser, so I added a condition to "ItemCondition" in ModStore.

Steps taken to verify a working solution:

• Having Iron Mass in main hand gives the skeletons the weapon as before, as well as off hand not giving the weapon.
• Removed the DUMMY mod so config option only shows up when Iron Mass is in main hand now.
• If you have another mod that uses the same config, it won't apply the triple damage to skeletons when toggled because we require "The Iron Mass, Gladius" to be in the main hand slot.
• "20% more damage if you have hit with your main hand weapon recently" will have the config appear with Iron Mass in offhand, and properly not give the triple damage.

Link to a build that showcases this PR:

https://pobb.in/SzAJuJj2lVhI

[Wires77]

While I don't usually love hardcoding item names into the code, this one is already there and really does only make sense when it has the other mod anyway