CDK-489: Move DatasetRepository to the SPI

 * Moved DatasetRepository to org.kitesdk.data.spi.DatasetRepository
 * Moved RandomAccessDatasetRepository to org.kitesdk.data.spi.RandomAccessDatasetRepository
 * Added deprecated interfaces that inherit from the SPI versions
 * Deprecated DatasetRepositories
 * Removed uses of DatasetRepositories from the code and test code

Closes #158.