Fix filters with custom action result

In my last pull request I fixed error while using caching pages:
https://github.com/ChicagoBoss/ChicagoBoss/pull/423
by adding `cached_page` in `boss_web_controller_render:expand_action_result`.
It looks, that there is another atom `page` and that both of them should be directly passed from before_filter to middle_filter.
(in last pull request I stripped it: `{cached_page, CachedResult}` -> `CachedResult`,
which was a mistake).

I also think, that it is good idea to be able to pass custom atoms from before_filters to middle_filters
and this commit adds this.

I am sorry, but currently I don't have time to write tests in common test.