first draft of SPI tester
issue #62 Introduced Factory interface, that can be used to create new instances of the Class under test
Issue #62 Not binding <K,V> at the StoreTester level
Issue #62 added spi-tester module
Issue #62 Produce jar with spi-test qualifier in core module
Issue #62 Expose spiTestArtifacts configuration from core to allow impl to depend on it
Issue #62 clean up test skeleton to not cause failures