Added user role location

[jydmnd]

Does this close any currently open issues?
Yes, issue #58

Any other comments?
Not sure if it is the right way to implement this, but it works for my needs.

Where has this been tested?
Operating System: Mac OS X Mojave
WordPress Version: 5.2.3

[sannefoltz]

Hi, I checked your code, i think it would be very useful feature, i saw an issue in it though.

$field_groups = array_unique( array_merge( $field_groups, $field_role_groups ), SORT_REGULAR );

If the same field group is attached to multiple roles, a duplication of field names exists. (You cannot register duplicate fields on the same Type.) So this array_unique() solved it. Could this still be merged? @jydmnd @jasonbahl Thank you for all work!