Update fields, cleanup text.

[growdev]

Related to #7. Refactor how entries are sent over.

Line 350 of /admin/class-convertkit-pmp-admin.php combines first and last names before sending to Convertkit. Convertkit has changed to use the name field as only the first name for each person. I’m hoping you can update the plugin to reflect this change.
Also, since I’m here the admin form language references adding a form, but this field was removed from the admin. It reads, “Add your API key below and then choose a default form to add subscribers to.” when it should be “Add your API key below.”

ref: https://wordpress.org/support/topic/name-update/