[Lua] Fix default isParty logic for battlefield addEssentialMobs

[TracentEden2]

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What does this pull request do?

This PR changes the default isParty to true for the battlefield function addEssentialMobs. This is needed because despite the default for addEssentialMobs being superlink = true the mobs will not superlink unless they are in the same party. Therefore, the current situation is that in some BCNMs (for example wings of fury and probably others) that use addEssentialMobs you can pull one mob at a time (which should not be possible). I do not know of any BCNMs where the mobs should not superlink, but if so these can be coded without using addEssentialMobs. I have discussed the change with @jmcmorris already and he thinks it is logical.

The PR also fixes a small related issue with Central Temenos 2nd floor where isParty is misspelled as inParty.

Steps to test these changes

Enter BCNM wings of furry and pull a Furries from the back and watch that the mobs superlink now