User Settings: Rename Experiments to Nostr

And use a nostr icon

spec/requests/settings_spec.rb

@@ -7,9 +7,9 @@ RSpec.describe "Settings", type: :request do
     login_as user, :scope => :user
   end
 
-  describe "GET /settings/experiments" do
+  describe "GET /settings/nostr" do
     it "works" do
-      get setting_path(:experiments)
+      get setting_path(:nostr)
       expect(response).to have_http_status(200)
     end
   end