Add sharec context to stub fulcrum with a form

Need this now so that record creator and updater pass, since they hit
the API and need a response.
Replace a method in Form

Replace Form#field_key_name_mappings with #find_field_by_key.
Update specs to reflect this.
Add RecordData::Extractor

This will pull the applicable record data out from the record's form
values.
Only supports TextField at this time.
This is a first pass at the implementation.
Update RecordData to pull data from form values

Issue #4.
Use RecordData::Extractor to get the data from the form values and
insert it as a column on the record.
Update specs to cover the TextField use case.
Will expand to cover other field types.