limit rainviewer to maxZoom level 7

this will be required starting January anyhow, see
https://www.rainviewer.com/api/transition-faq.html

already removed the rain layer in a past commit because it wasn't
working anymore
seems the radar layer with maxZoom 7 should stay working but i guess
i'll have to check for alternatives if it does not

the rate limit starting january should work ok with maxZoom 7 unless you
zoom into a lot of regions

html/layers.js

@@ -794,7 +794,7 @@ function createBaseLayers() {
                 url: 'https://tilecache.rainviewer.com/v2/radar/' + latestLayer.past[latestLayer.past.length - 1].time + '/512/{z}/{x}/{y}/6/1_1.png',
                 attributions: '<a href="https://www.rainviewer.com/api.html" target="_blank">RainViewer.com</a>',
                 attributionsCollapsible: false,
-                maxZoom: 10,
+                maxZoom: 7,
             });
             rainviewerRadar.setSource(rainviewerRadarSource);
         };