Add Variable Settings to the Back End of the Study Custom Post Type

[mikepsinn]

First commit the plugin to the repo.

Then use this javascript for adding the new fields:
https://github.com/mikepsinn/QuantiModo-WPLMS/blob/8dafd372944609a1ae3a4bb739a24e672c418495/wp-content/themes/wplms-qm/js/_variable_settings.js