Fix clang style errors in rtp_rtcp and dependant targets

Mark functions with override instead of virtual.
Add explicit non-trivial constructors/assign operators/destructors.
Define them in .cc files instead of inlining
use auto* instead of auto when deduced type is raw pointer

Bug: webrtc:163
Change-Id: I4d8a05d6a64fcc2ca16d02c5fcf9488fda832a6d
Reviewed-on: https://webrtc-review.googlesource.com/48781
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21927}

modules/rtp_rtcp/source/rtp_receiver_impl.h

@@ -35,7 +35,7 @@ class RtpReceiverImpl : public RtpReceiver {
                   RTPPayloadRegistry* rtp_payload_registry,
                   RTPReceiverStrategy* rtp_media_receiver);
 
-  virtual ~RtpReceiverImpl();
+  ~RtpReceiverImpl() override;
 
   int32_t RegisterReceivePayload(int payload_type,
                                  const SdpAudioFormat& audio_format) override;