Adjusting rendering options for SimpleForm

By changing the form builder from `use :input` imperative, I'm instead
wrapping the input call with the aria-labelledby and aria-describedby.

This is not a bullet-proof solution but delivers on what was
requested.

The included test is for a reference implementation and may not be
reflective of the full test that we are after.

References DLTP-324
Merge pull request #172 from ndlib/DLTP-324-aria-describedby

Adjusting rendering options for SimpleForm