Sparkmeasure

This release has minor improvements.
Updated and extended the list of shuffle metrics.
Improved output of taskMeasure.
Note: this release breaks the compatibility with Spark 2.1 and 2.2. Use for Spark 2.3 and higher only.

Minor improvements in this release.
Updated InfuxDB sink to map executorId, executorHost with the InfluxDB sink. This is used by the Spark dashboard as detailed in [Spark dashboard annotations](https://github.com/LucaCanali/Miscellaneous/tree/master/Spark_Dashboard#spark-metrics-dashboard-with-queryjobstage-annotations)

This release extends sparkMeasure Flight recorder mode with an InfluxDB sink:
- It allows to write Spark queries, jobs and stages information to InfluxDB.
- Optionally it can write stage and task metrics to InfluxDB.
- These features have been added to improve Spark performance dashboard built with Grafana and InfluxDB.

Main changes with this release are the refactoring of the Flight Recorder mode.
Tested with Apache Spark up to version 2.4.3 and for Scala 2.11 and 2.12.

This release merges a few PRs I received, adds a Python API package wrapper for PySpark and has improved documentation and examples.