Added party alliances

Adds the following commands:
`/party alliance`
`/party alliance invite <target>`
`/party alliance accept`

Allies will share party chat and will not be able to harm eachother.
Item and XP sharing is limitied to a single party. Allowing two parties
to team up without sharing resources and XP.

#1009
Added Party levels
Party unlock levels
expshare = xpshare
Add option to inform all party members
Even more options, only count shared XP

This means that you can only level a party if two or more party members
earn XP while near eachother.
Fix this bug
Colouring party! :D
Represent the unlocked/locked features