Add new settings tab for participation processes

- Rename setting keys
- New tab por participation processes
- Hide these settings from features tab

spec/features/admin/hidden_proposals_spec.rb

@@ -8,13 +8,11 @@ feature "Admin hidden proposals" do
   end
 
   scenario "Disabled with a feature flag" do
-    Setting["feature.proposals"] = nil
+    Setting["process.proposals"] = nil
     admin = create(:administrator)
     login_as(admin.user)
 
     expect{ visit admin_hidden_proposals_path }.to raise_exception(FeatureFlags::FeatureDisabled)
-
-    Setting["feature.proposals"] = true
   end
 
   scenario "List shows all relevant info" do