Add onLocationChange.fitView config option

It defaults to false now, which is a change - this seems like a sensible
choice though. I can see how it would be annoying to have the map change
while looking at it just because *something* moved.

Fixes #41.

src/views/Map.vue

@@ -232,7 +232,9 @@ export default {
   },
   watch: {
     lastLocations() {
-      this.fitView();
+      if (this.$config.onLocationChange.fitView) {
+        this.fitView();
+      }
     },
     filteredLocationHistory() {
       this.fitView();