Prevent KeyError when page_template not supplied

When `page_template` is not supplied as a kwarg via `.as_View()` a
KeyError is raised because `.pop()` is used on a dictionary with no
default value specified.
Merge pull request #42 from jnns/patch-1

Prevent KeyError when page_template is not supplied.
Add test for a customized ListView.
Avoid django.conf.urls.default deprecation warning.
Merge pull request #2 from frankban/master

sync with main repo