Implement API for external access

[johanneshiry]

In order to use OSMoGrid as module e.g. in NetPad++ a simple API would be helpful. The main purpose of this API should be to spin up an OSMoGrid run using a config and to return a GridInputContainer instance. Several approaches (e.g. queue, akka ask, plain future, plain methods, ...) can be considered to achieve this. A final decision should be made after a first discussion about the API details.