Percentage based maximum hostile cull and aggression factors

Changed the maximum monsters to cull so that this is a percentage of the total number of monsters in a world, rounded down. This is set to 5% in the config here. The aggression factor also changes as a percentage of the limit rather than an absolute number, to avoid these figures being too large for the End.

For example, if I have 100 monsters in the world and a current limit of 80, we have a maximum cull of 5 per run. We'll cull 5 on the first run, then 4 at a time (since now below 100) until we have 80 or fewer.

In the End, if I have 32 monsters and a current limit of 24, at most 1 monster will be culled per run until we're at that limit.

The current limit is based on the spawn limits and fluctuates with the moon phase to keep mobs moving around a bit. This change alters the cycle from limit-10 to limit+30 and instead makes it 90% to 120% of the spawn limit. This again stops the figure from becoming excessively low on a per-player basis in the End.

Package of this is at https://github.com/pruby/MusterCull/blob/package/MusterCull-20140618.jar - not in pull as keeping JARs in the main git branch grows the repo size permanently - includes every version ever.

Recommend reloading the config from this repository after pull - MusterCull/config.yml.