Beam / LLCP improvements.

- Don't show Beam UI unless the other device runs a SNEP server.
  We didn't do this previously because an old stack issue could
  delay the SNEP connect by as much as 750ms, therefore also
  delaying the UI. We expect there to be very few of those devices
  in use at this point (if any).
  This also paves the way for preventing Beam UI to be shown when
  connecting to future Android devices (those devices could shut down
  SNEP in specific scenarios).
- Immediately try to connect LLCP (SNEP, handover) services.
  We didn't do this previously because the old stack had race conditions,
  which could be triggered by immediately sending a LLCP connect.
  Again, very few of those devices are expected to be in use
  at this point.
  Making this change will generally decrease the latency of a P2P
  transaction, especially in scenarios where the send was previously
  authorized (ie from the share menu).
- Fixed a bug in SendUi where it wouldn't store the screenshot in
  a specific case. We're only hitting this now because of the two
  changes I mentioned above.
- A bit of clean-up (though this class could use a lot more...)

Change-Id: I52f5ff314dc06e5502bdf869ee658078c3a44fde