Fine tune UI of package installer.

This fixes two screens in the case no permissions are required.
- Do not remove tabs, just make them invisible. This is required to push
  the "OK" and "CANCEL" button to the bottom
- Show spacer under text as this looks prettier.

Fixes: 28746145
Change-Id: Ia312b476c7e3944709ed3f8fd71d12268559257f