Let shopping tabs listen to URL changes

When clicking on a shopping tab like "contact", it changed the URL. But
changing the URL did not change the tab. Listening to URL changes
enables manual manipulation of the URL and simple links to "#/contact"
to open the contact tab.

app/assets/javascripts/darkswarm/controllers/shopping_tabs_controller.js.coffee

@@ -1,4 +1,4 @@
-Darkswarm.controller "ShoppingTabsCtrl", ($scope, $controller, Navigation) ->
+Darkswarm.controller "ShoppingTabsCtrl", ($scope, $controller, Navigation, $location) ->
   angular.extend this, $controller('TabsCtrl', {$scope: $scope})
 
   $scope.tabs =
@@ -6,3 +6,7 @@ Darkswarm.controller "ShoppingTabsCtrl", ($scope, $controller, Navigation) ->
     producers: { active: Navigation.isActive('/producers') }
     contact: { active: Navigation.isActive('/contact') }
     groups: { active: Navigation.isActive('/groups') }
+
+  $scope.$on '$locationChangeStart', (event, url) ->
+    tab = $location.path().replace(/^\//, '')
+    $scope.tabs[tab]?.active = true

app/views/shop/_messages.html.haml

@@ -10,7 +10,7 @@
              register: ('<a auth="signup">' + t('.register') + '</a>').html_safe}
         - else
           = t '.require_customer_html',
-            {contact: ('<a href="##contact">' + t('.contact') + '</a>').html_safe,
+            {contact: link_to(t('.contact'), '#contact'),
              enterprise: current_distributor.name}
 - elsif @order_cycles and @order_cycles.empty?
   - if current_distributor.preferred_shopfront_closed_message.present?