Add Proxy and Add Sponsor Buttons are Reversed

Steps to repro:

1. Log into folio-snapshot as diku_admin
2. Go to Users and pick any active user
3. Edit user record and scroll to the proxy section

Actual: Buttons are reversed

Expected:

Let's clarify things by changing the wording of the headers and the button labels:

• "Block, Madison is proxy for" should be changed to "Sponsors (Madyson Block can borrow on behalf of these people)"
• Add proxy button should be changed to "Add"
• "Block, Madison is sponsor for" should be changed to "Proxies (these people can borrow on behalf of Madyson Block)"
• Add sponsor button should be changed to "Add"