First steps at supporting other map tile servers (#7)

src/store/map.ts

@@ -18,10 +18,12 @@ export const zoom0 = 18;
 export interface MapScope {
   center: geoPoint;
   zoom: number;
+  tileProvider: string;
 }
 var initialMapScope: MapScope = {
   center: { lat: -37.8403508, lon: 77.5539501 },
   zoom: 15,
+  tileProvider: 'osm',
 };
 
 // Derived properties
@@ -197,6 +199,9 @@ const mapSlice = createSlice({
   name: 'map',
   initialState: initialMapState,
   reducers: {
+    setTileProvider: (state, action) => {
+      state.scope.tileProvider = action.payload;
+    },
     resize: (state) => {
       evaluateStateFromScope(state);
     },