Support g51v2 (CTO Unsynchronized)

[emgre]

Closes #124.

• DNPTime now has a TimestampQuality attached to it. By default, it is set at TimestampMode::INVALID.
• When building g2v3 and g4v3 responses, the proper g51 variation is used to according to the timestamp quality.
• Flags now has an explicit constructor. Otherwise, it led to wrong calls when updating binary input values (because bool is synonym of uint8_t on some platforms)
• Test procedure 8.15.2 of the certification procedures were executed to confirm proper handling (also added to dnp4s).
• Renamed IIN1.0 from ALL_STATIONS to BROADCAST, because that's its name in the spec.
• Renamed TimestampMode to TimestampQuality.
• Added -Wextra in CircleCI (closes run circle CI builds w/ additional CXX flags #307).
• Added comment about FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION (closes expose option to disable CRC checking when fuzzing #306).

[codecov]

Codecov Report

Merging #316 into develop will decrease coverage by 0.89%.
The diff coverage is 44.79%.

@@            Coverage Diff             @@
##           develop     #316     +/-   ##
==========================================
- Coverage    46.77%   45.87%   -0.9%     
==========================================
  Files          492      493      +1     
  Lines        21418    21456     +38     
==========================================
- Hits         10018     9844    -174     
- Misses       11400    11612    +212

Impacted Files	Coverage Δ
cpp/lib/src/app/GroupVariationRecord.h	100% <ø> (ø)	⬆️
cpp/lib/src/link/CRC.cpp	100% <ø> (ø)	⬆️
cpp/lib/include/opendnp3/app/IINField.h	93.33% <ø> (ø)	⬆️
cpp/lib/src/outstation/StaticDataMap.h	51.09% <0%> (ø)	⬆️
cpp/lib/src/master/MeasurementHandler.h	81.72% <0%> (-2.82%)	⬇️
cpp/lib/src/decoder/DecoderImpl.cpp	0% <0%> (ø)	⬆️
...p/lib/include/opendnp3/master/PrintingSOEHandler.h	0% <0%> (-93.91%)	⬇️
cpp/lib/src/gen/TimestampQuality.cpp	0% <0%> (ø)
cpp/lib/src/app/BinaryCommandEvent.cpp	86.66% <0%> (ø)	⬆️
cpp/lib/src/app/QualityFlags.h	0% <0%> (ø)
... and 34 more

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