Release candidate 8

Refactored metric interfaces slightly;

1. All confidence dependent metrics are now of "plot type" - meaning that a single metric instance can work with several confidence levels at the same time.
2. Grid search now allows both SingleValuedMetric and PlotMetric types for both the optimization metric and secondary metrics (that are reported next to the optimization metric). For the optimization metric only a single evaluation point (i.e. confidence level in most cases) are allowed for this metric, but the secondary metrics can have several evaluation points. A new potential use-case can be optimizing for Observed Fuzziness for a conformal classifier model (i.e. confidence independent) but having secondary metrics to report model calibration, AverageC and proportion single-label predictions for several confidence levels - which might give more insight than the Observed Fuzziness value alone.
3. At the API level there are some name changes to metric classes to streamline the getName() methods with the class names, to simplify things. The names are kept from the CLI perspective to not break any code (i.e. the output from the getName() methods are kept, but class names have changed).

All changes are listed in the changelog.

Thin jars can be pulled from Maven central using the new version 2.0.0-rc8, e.g.:

<dependency>
    <groupId>com.arosbio</groupId>
    <artifactId>cpsign-api</artifactId>
    <version>2.0.0-rc8</version>
</dependency>