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.

Closes #1009
Added party levels

Parties now have XP and Levels. Party features such as party teleport and party chat have to be unlocked before they can be used by the party members
Changed appearance of party member list