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/rtcp_sender.cc

@@ -92,7 +92,7 @@ class PacketContainer : public rtcp::CompoundPacket {
  public:
   PacketContainer(Transport* transport, RtcEventLog* event_log)
       : transport_(transport), event_log_(event_log) {}
-  virtual ~PacketContainer() {
+  ~PacketContainer() override {
     for (RtcpPacket* packet : appended_packets_)
       delete packet;
   }