Replace login_required decorator with a validating one

This one will validate that the url is under /accounts/, which is
the only part we are going to be excluding from caching once we
move the website to https-only.

pgweb/profserv/views.py

@@ -1,6 +1,6 @@
 from django.shortcuts import render_to_response
 from django.http import Http404
-from django.contrib.auth.decorators import login_required
+from pgweb.util.decorators import login_required
 
 from pgweb.util.contexts import NavContext
 from pgweb.util.helpers import simple_form