Refactor functionality from OLMapManager to FeatureManagers

[Nils1729]

Currently, the OLMapManager has accumulated lots of code that registers layers, interactions and ElementManagers to the map. This is not only messy but also stands against the idea of FeatureManagers managing everything that is relevant for specific to features.

Ideally I want OLMapManager to only

1. Create and configure the Map
2. Instantiate a collection of FeatureManagers and let them configure the map to their needs. They should add the layers, ElementManagers and interactions themselves.