Add Procfile.dev
wip: Add fields to agreement

* Failing spec
Create Field and AgreementField models
Relaxed the uniqueness validation so we can update existing agreements.
Add columns fields.enabled_by_default, agreement_fields.enabled
Provide default fields in db:seeds.  Use in tests.
Agreement accepts nested agreement_fields
Fix routes to allow both repo names with periods as well as .csv format.

* Consider paths:

  /agreements/jasonm/beerfire.com
  /agreements/jasonm/beerfire.com.csv
Agreement can #build_default_fields, supersedes #create_default_fields
Specify fields when creating an Agreement
Accept configurable fields for agreements
Consistently order agreement fields and field entries
Add Field#description.  Add "Corporate Contributor Information" field.