Changed /course/install to /courses/install.

refs #16137
Merge branch 'bug/16137' into develop
api: Added identifier to <object>/add response.

This is used to identify what we use as the option text for
the object_list when adding/updating/deleting objects.

refs #16065
update_models: Updated add <object> functionality.

Now, when adding an object, the 'Add' button is changed to a
'Submit' and a blank <option> is created. We are still able to use
the 'Update' button to add a district, as to not get rid of previous
functionality.

refs #16065
Merge branch 'bug/16065' into develop
register: Added 'btn' class to 'Add User' button.

refs #16173
Merge branch 'bug/16173' into develop
css: Removed zocial.css where it isn't used.

refs #16167