Bug 861227 - recipients search results are hidden message input text takes available screen

https://bugzilla.mozilla.org/show_bug.cgi?id=861227



- create dedicated recipient results element
- shift logic from previously shared container to new dedicated element
- innerHTML => textContent
- Rename ThreadUI.searchContact => ThreadUI.recipientSearch (matches the ThreadUI.reci
- Wrap the recipient search result discarding operations (clear and hide) in a functio
- Tests display of ThreadUI.recipientResults by ThreadUI.recipient.value
  - has value, is not cleared or hidden
  - no value, is cleared and hidden
- Tests discarding results with ThreadUI.recipientSearch.discard()