Fix local store detection and related issues

- Add localStore into the stash because it's used in templates
- Hide the Channels button for non-local stores because the link 404s
  anyway
- Fix a style issue when having popovers in dark mode

src/lib/Hydra/Controller/Root.pm

@@ -57,6 +57,7 @@ sub begin :Private {
     $c->stash->{tracker} = defined $c->config->{tracker} ? $c->config->{tracker} : "";
     $c->stash->{flashMsg} = $c->flash->{flashMsg};
     $c->stash->{successMsg} = $c->flash->{successMsg};
+    $c->stash->{localStore} = isLocalStore;
 
     $c->stash->{isPrivateHydra} = $c->config->{private} // "0" ne "0";