[core] changes to enable folding YCSB-TS back into YCSB (#1095)

• [core] Drop JDK 7 Support

Sets compiler target to 1.8
Additionally removes openjdk7 from travis build-matrix
Fixes #1033

Additionally includes lexicographic reordering of binding-dependency properties in root pom

• [core] introduce baseclass for timeseries database bindings

This base-class parses the queries generated by TimeSeriesWorkload into a format
that's usable for simple consumption.
The format has been defined through the work done by Andreas Bader (@baderas) in
https://github.com/TSDBBench/YCSB-TS.

• [core] parse debug and test properties for all Timeseries databases

• [core] Add method to define possible tagKeys for Timeseries Workloads

Some TimeSeries Databases require a "schema" up front.
To generate said schema, the tag keys used by the workload are required.
This method should be centrally available for maintainability

• [core] Provide default implementation for operation

TimeSeries databases only rarely support deleting data. As such we can generally assume
the operation to always return a Status.NOT_IMPLEMENTED. Similarly to updating that trivial
implementation does not need to be repeated in every TimeSeriesDatabase implementation

• [core] Address review

This adds a copyright header and significant amounts of javadoc for TimeseriesDB
Furthermore occurrences of Long have been largely replaced with the primitive long
Finally an overload for signed integer values has been added for insertions