Add an iLevel requirement to join BGs

Like the title suggests, add an iLevel requirement to join Battlegrounds. Right now there is rarely any point in doing one since it is dominated by low geared characters. I doubt it only happens on Icecrown, but I am currently talking from that realm's perspective.

The current state of Battlegrounds is highly based on RNG, you either join a team from what 30-50% consists of lower iLevel characters or you fight against one. Either way there is no fun or excitement included with it.

https://www.warmane.com/devlog

"We will also look into the functionality of separating lower and higher geared players in battlegrounds. We have heard your feedback but as the system might have significant effects on battleground queues, we are unable to determine whether this will become a feature for sure."