Pass a new _req template variable

Provide all the templates with a new `_req` variable
that holds the original web request so that template
can use query and post params directly.

There are situations where it is much more straightforward
than to pass the specific parameters via controller
all the time again and again, across the whole application.
Merge pull request #333 from ztmr/ztmr/dtl_req_var

Pass a new _req template variable
Fix before_ -> 'ok' in Elixir controllers
Fix {ok, ...} return values from before_