Parses view fields from request into a given
object. The 'form-view-field-parser' slot of each field is used to
parse a string obtained from the request into an appropriate
value. The generic function 'parse-view-field-value' is called to
invoke the parser.

If this function succeeds updating the object with all fields obtained
from the request, it returns true. Otherwise returns nil as the first
value, and an association list of fields and errors as the second
value.

The function uses 'form-view-persist-p' to determine whether the
object is to be persisted. If so, it calls 'persist-object'.

Specialize this function to parse given objects differently.