Add new field identifier for Extended Client Fields #7
Description
An update to this module is needed to support a new Core feature added in 3.0.13:
formtools/core#472
Since we'll want to scope the placeholders used in the Core fields (e.g. {$extended_client_fields.fieldX}, or something less verbose) let's use the same convention as with Custom Fields and call the new setting for each field "field identifier". Then add a new page in the module UI that lists all placeholders so the user can copy & paste.