Enable exception throwing from jobs

Just "throws Exception" so we can catch anything coming out. If you want
to error handle yourself, catch in your job, otherwise the exception
will bubble out of EntitySystemInterface.execute.
IDE files
Add parametrized jobs

Create Parametrized job that takes a generic input and offer a method
on EntitySystemInterface that takes it.
Status object, Javadoc, cleanup

Provide a method to get a EntitySytem.Status class reporting the current sizes
of maps, pretty-printing itself on toString().

Clean up code a little by creating packages for the different concepts, sort
entity system methods API by similarity.

Add package.html files.