[untracked] handling ndn-cpp exceptions
[untracked] code cleanup

- removed deprecated code
[untracked] playback latency

- implemented simple latency calculation: producer publishes unix
timestamp for each packet alongside with the other metadata. consumer
can use this timestamp at playback time for calculating approximate
playback latency. this value is reliable only if producer and consumer
are ntp-synchronized.
[untracked] fixed rebuferrings caused increased latency

sometimes after rebuffering - old data was fetched which caused bigger
latency than it was before.
[untracked] fixed playout timings, skipping out-of-order frames

- in conditions of frames scarcity, inferred playback time was not
calculated and considered properly. fixed this.
- implemented skipping delta frames from wrong GOP (in case if delta
frame was acquired earlier for playback than it's corresponding
keyframe)
[untracked] added rtf estimation output into statistics window
[untracked] minor fixes
[untracked] added python script for convenient logs filtering
ndnrtc v0.8.0-alpha