[https://github.com/coto/gae-boilerplate/issues/279] Make bp_includes.lib.basehandler share jinja2_factory with bp_includes.lib.error_handler.

Issue 279 is happening because error_handler (bp_includes/lib) is not initializing Jinja with the factory function provided by basehandler (called jinja2_factory). I split out generate_csrf_token and jinja2_factory from basehandler into a separate module, included it in both basehandler and error_handler, and that fixes the abovementioned behavior on our site.

Unit tests all succeed with the change.

Please let me know if you need any additional information or confirmation. Many thanks for creating the boilerplate project; it has been very useful.