Update the attack meta

The current attack meta is unintuitive as larger players can be given too much of an advantage. It also makes it very difficult for multiple smaller nations to gang up on the crown.

We should keep the following:

1. Larger attacks should give a troop loss boost to reward & encourage a single large attack vs many tiny ones.
2. The meta must change slowly over time. The initial meta should be fairly similar to the current one, and we update it to the desired meta after several releases.