Added a configurable option for pjax

Some actions, like logging in as another user, should be rendered
in the app, not via pjax.  This change allows an action to indicate
how it should be rendered.

app/helpers/rails_admin/application_helper.rb

@@ -114,7 +114,7 @@ def menu_for(parent, abstract_model = nil, object = nil, only_icon = false) # pe
         wording = wording_for(:menu, action)
         %{
           <li title="#{wording if only_icon}" rel="#{'tooltip' if only_icon}" class="icon #{action.key}_#{parent}_link #{'active' if current_action?(action)}">
-            <a class="#{action.key == :show_in_app ? '' : 'pjax'}" href="#{url_for({ :action => action.action_name, :controller => 'rails_admin/main', :model_name => abstract_model.try(:to_param), :id => (object.try(:persisted?) && object.try(:id) || nil) })}">
+            <a class="#{action.pjax? ? 'pjax' : ''}" href="#{url_for({ :action => action.action_name, :controller => 'rails_admin/main', :model_name => abstract_model.try(:to_param), :id => (object.try(:persisted?) && object.try(:id) || nil) })}">
               <i class="#{action.link_icon}"></i>
               <span#{only_icon ? " style='display:none'" : ""}>#{wording}</span>
             </a>

lib/rails_admin/config/actions/base.rb

@@ -39,6 +39,11 @@ class Base
           false
         end
 
+        # Render via pjax?
+        register_instance_option :pjax? do
+          true
+        end
+
         # This block is evaluated in the context of the controller when action is called
         # You can access:
         # - @objects if you're on a model scope

lib/rails_admin/config/actions/show_in_app.rb

@@ -21,6 +21,10 @@ class ShowInApp < RailsAdmin::Config::Actions::Base
         register_instance_option :link_icon do
           'icon-eye-open'
         end
+
+        register_instance_option :pjax? do
+          false
+        end
       end
     end
   end