Adds the ability to mark (Sub)Menu's 'active'.

But it does not happen automatically. You must set SubMenu.active = True or Menu.active = True.
Apply hover effect to all parent menus not just the first.
Merge pull request #3257 from mkoistinen/Updates_for_3251

Adds the ability to mark (Sub)Menu's 'active'.
Remove leftover test styles
Merge pull request #3258 from divio/Fix_hover_effect_for_deeper_menus

Apply hover effect to all parent menus not just the first.
Improve the subclass-ability of the RenderPlugin templatetag.
Merge pull request #3261 from divio/refactor_render_plugin_tag

Improve the subclass-ability of the RenderPlugin templatetag.
Ensure that __str__ really only returns text (unicode)
Add test to ensure moving or deleting AliasPlugins works
Merge pull request #3265 from divio/force_text_for_AliasPluginModel

FIxes #3264