Changes to EconomyService

This commit adds additional javadocs telling that the implementation of
the EconomyService must be thread-safe.

This commit also adds an abstract method for removing accounts.

Signed-off-by: XemsDoom <moser.luca@gmail.com>
Merge pull request #525 from Sleaker/master

Events for EconomyService
Added fake lighting manager for buffers with unknown managers
Merge pull request #512 from XemsDoom/economyservice

Changes to EconomyService