Support soft-updating through update links

Where "soft-updating" means updating from CDNs, and "hard-updating"
means updating from `ublockorigin.github.io/uAssets`.

src/js/messaging.js

@@ -2072,7 +2072,7 @@ const onMessage = function(request, sender, callback) {
             url: 'dashboard.html#3p-filters.html',
             select: true,
         });
-        io.updateStart({ delay: 100 });
+        io.updateStart({ delay: 100, auto: request.softUpdate });
         break;
 
     default:

src/js/scriptlets/updater.js

@@ -55,6 +55,7 @@ function updateStockLists(target) {
         vAPI.messaging.send('scriptlets', {
             what: 'updateLists',
             listkeys,
+            softUpdate: updateURL.searchParams.get('soft') && true || false,
         });
         return true;
     } catch (_) {