Extract the world configuration outside of the world

This allows us to customize the dynflow world from Foreman/other
plugins. Also, not we don't have to create custom world class for us,
and the DynflowConfiguration class should be more explanatory, than
just passing a hash.

Also, it's worth considering adopting this approach of world
configuration in Dynflow core: configuration object producing the
world instances with given configuration. We could get rid of the
Dynflow::SimpleWorld as well, and just have default configuration
implementation.
Better organization of dynflow-related stuff

Besides better structure, it also makes sure the world initialization
happens after all engines were able to influence the dynflow
configuration.

From now on, to specify that another engine requires dynflow runtime,
it should call `ForemanTasks.dyntask.require!` instead
of `ForemanTasks.dyntask.initialize`.
Remove unused code
Merge pull request #3 from iNecas/init-refactor

Better organization of dynlfow related stuff