Need way to enter URI prefix when adding a registry

[cjmyers]

This is needed when testing with a local SynBioHub

[cjmyers]

When you Add Registry, add another entry called Registry Prefix. When you enter a value into Registry URL, it should be auto-copied into Registry Prefix. The Registry Prefix should not be editable by default. Add a button labeled "Edit" next to Registry Prefix entry. When you select Edit, pop up a window that says "The Registry URL and Prefix should normally be the same value. These usually only differ when you are debugging using a local registry. Are you sure you want to edit the prefix?" This pop-up should have buttons "Yes" and "No". If you select "Yes", make the Registry Prefix editable. If you select "No", do not make it editable.