XP changes

2X XP is here! Alistair has confirmed that the XP progress rate will now be 2X. This means that the rate is doubled compared to the same amount previously awarded for each action. There will not be an XP wipe on Facepunch or Rustafied servers, though individual server owners may choose to wipe XP. Garry has removed all remaining traces of the XP system from the prerelease branch.