sinatra runner: pass the logger as a template local; remove from scope

This removes the `logger` method from the template scope and switches
to exposing it to the template as a local.  This is prep for moving
away from Sinatra for template rendering.  Not all template engines
will want to use a pre-defined scope so the scope is being deprecated.

@jcredding ready for review.
@kellyredding - This is correct, but I think this is comparing 2 `nil` values. That's why it didn't fail with `deas_logger` in there. We might consider setting a logger to some value, if possible, to avoid the `nil == nil`.