Added worker pool.
Merge branch 'marcelog_dynamic_dependencies_6' into inaki.worker_pool

Conflicts:
	rebar.config
	src/sumo_db.app.src
added storage backend concept
Removed debug lagers.
Merge branch 'master' into inaki.worker_pool
PR corrections
Merge pull request #31 from inaka/inaki.worker_pool

Inaki.worker pool