Added count parameter to summon and properly checks for invalid parameters

[12xx12]

I just wanted to summon multiple entities at once... Now the core plugin can do this.

And I noticed that you could enter 3 additional parameters. The additional parameter would be ignored, but no error was shown. I rephrased the check to be more understandable (hopefully)

[mathiascode]

Keep in mind that the command should resemble the vanilla equivalent, or at the very least allow for running vanilla commands without conflicts. The count parameter currently occupies the slot for NBT data. Although we don't support NBT tags at the moment, support should be introduced at some point.

[12xx12]

Hm.. You are right. I'm gonna keep the rephrasing of the Split Check