Add template "theme" feature, albeit global

would be even better to let each user session have something different, but
alas this is all-or-nothing for now

tailbone/views/common.py

@@ -42,6 +42,7 @@ import tailbone
 from tailbone import forms
 from tailbone.db import Session
 from tailbone.views import View
+from tailbone.util import set_app_theme
 
 
 class Feedback(colander.Schema):
@@ -125,6 +126,22 @@ class CommonView(View):
             ('Tailbone', tailbone.__version__),
         ])
 
+    def change_theme(self):
+        """
+        Simple view which can change user's visible UI theme, then redirect
+        user back to referring page.
+        """
+        theme = self.request.params.get('theme')
+        if theme:
+            try:
+                set_app_theme(self.request, theme, session=Session())
+            except Exception as error:
+                msg = "Failed to set theme: {}: {}".format(error.__class__.__name__, error)
+                self.request.session.flash(msg, 'error')
+            else:
+                self.request.session.flash("App theme has been changed to: {}".format(theme))
+        return self.redirect(self.request.get_referrer())
+
     def feedback(self):
         """
         Generic view to present/handle the user feedback form.
@@ -188,6 +205,12 @@ class CommonView(View):
         config.add_route('mobile.about', '/mobile/about')
         config.add_view(cls, attr='about', route_name='mobile.about', renderer='/mobile/about.mako')
 
+        # change theme
+        config.add_tailbone_permission('common', 'common.change_app_theme',
+                                       "Change global App Template Theme")
+        config.add_route('change_theme', '/change-theme', request_method='POST')
+        config.add_view(cls, attr='change_theme', route_name='change_theme')
+
         # feedback
         config.add_route('feedback', '/feedback', request_method='POST')
         config.add_view(cls, attr='feedback', route_name='feedback', renderer='json')