Implemented parties

I implemented parties today.

This was quite a lot more work than I expected, because of all the edge cases which needed to be taken care of. Handling party requests of people who log out, handling parties disbanding while taking on new members, removing members who are online, offline or in char select... all sources of annoying bugs. The good news is that I will likely be able to re-use most of the code when it will come to guilds later.

Parties don't affect exp sharing because that's not needed in my current system - every attacker gets his full exp share anyway.

What parties do instead:

• Party members share private instances
• Party members can chat with each other
• Party members can see each others location