Changes in UI and minor extra functionality for rtp_analyzer.

1. The tool now displays packet loss in %.

2. It can print header information to stdout like rtp_analyze.

3. It has a command-line switch that lets you override the sample rate
guessing. With the flag "--query_sample_rate" the tool asks you to
always provide a sample rate.

4. Less decimals are printed for the estimated sample rate.

NOTRY=True

Review-Url: https://codereview.webrtc.org/2123773002
Cr-Commit-Position: refs/heads/master@{#13385}

webrtc/tools/py_event_log_analyzer/pb_parse.py

@@ -28,6 +28,7 @@ class DataPoint(object):
     (first2header_bytes, self.sequence_number, self.timestamp,
      self.ssrc) = header
     self.payload_type = first2header_bytes & 0b01111111
+    self.marker_bit = (first2header_bytes & 0b10000000) >> 7
 
 
 def parse_protobuf(file_path):