DONE: split map from data

Situation
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dataservice --has--> layergroups --has--> layers. Everything in the app is dependent on this mechanism to get data, and this mechanism is dependent on Leaflet and the map. This makes that we always need leaflet anywhere in nxt. We could change this.

Actions
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- [x] Move synctime and map related methods of layergroup to nxt-map.
- [x] Move all the map related stuff in the *-layer-services to a generic map-layer-service.
- [x] Add callbacks to DataService that enable the mapService to perform actions on opacity change, layergroup toggles and double clicks on data-menu items.

Results
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This gives us a separate *data-menu* component which contains all data layers and layergroups under the menu-ui-component. And we have a *map* component which contains all the map related logic under the map-ui-component. 

The map component is fully optional. The data-menu is a dependency of the box, the timeline and the map.