Fix up 'add to blacklist' button behaviour

- Don't crash in landscape, as button isn't present in landscape layout
- Only show it for incoming calls with number (it makes no sense to
  blacklist outgoing calls, and calls without number can't be
  blacklisted on a per-call basis anyway)

JIRA: CYAN-865
Change-Id: Ie98e09abc4f4e62e67ccf12322e2a0cea0e26d60