userportal,webadmin: Replace UIConstants.empty()

- Replaced UIConstants.empty() with "", instead of having
  a localized version of 'empty' which makes no sense and
  can in fact cause issues if the translation is not in fact
  empty.

Change-Id: I17fac230cd19dd3513df06de355171430a823257
Signed-off-by: Alexander Wels <awels@redhat.com>