Refactor dynamic UI field parsing a bit

Now it is possible to use deeply-nested dictionary keys 'name' and
'type' - because top-level 'name' and 'type' keys' processing is moved
out from the recursive `parse_spec` function.

Change-Id: Iffa37d551583011715d3b436e10ce8748e79d92c
Merge "Refactor dynamic UI field parsing a bit"