Add extra_stylesheets knob to Reddit.

This provides an easy way for plugins to add extra separate stylesheets
to the site.

r2/r2/lib/pages/pages.py

@@ -130,6 +130,7 @@ class Reddit(Templated):
     content_id         = None
     css_class          = None
     extra_page_classes = None
+    extra_stylesheets  = []
 
     def __init__(self, space_compress = True, nav_menus = None, loginbox = True,
                  infotext = '', content = None, short_description='', title = '', robots = None, 

r2/r2/templates/reddit.html

@@ -97,6 +97,10 @@
   <![endif]-->
 
   ${adminbar_stylesheet()}
+
+  %for extra_stylesheet in getattr(thing, 'extra_stylesheets', ()):
+    ${less_stylesheet(extra_stylesheet)}
+  %endfor
 </%def>
 
 <%def name="javascript()">