pipe the sinatra call settings to the view handler via `app_settings`

This exposes the sinatra call's settings via the `app_settings`
method on a view handler.  This is needed with the no singleton
version of Deas so that view handlers can access app configuration
values and settings.  Previously the singleton provided this access.

@jcredding ready for review.  biggest change here is changing the accessors on the runner to just readers.  I like this (it limits down the API), but unsure if anything using deas expects accessors.  All tests pass though, so there's that.