userportal,webadmin: Fix frontend compile fedora 21

- On java < 8 the missing class definition for GenericApiGWTServiceAsync
  was silently ignored and would not cause an issue, but with fedora 21
  you can't downgrade to java < 8 so the missing class would cause the
  compile to fail. The class is generated but we never added the generated
  classes path to the source definition in the POM.xml

Change-Id: Ib7fc9c9ecebf39dcae3a0b9c3923e2790dbb179a
Signed-off-by: Alexander Wels <awels@redhat.com>