Remove Flink dependency for store instance

[chpengzh]

GradoopStoreConfig instance maybe passed from process to process(flink driver to worker), for example, I can create a store instance in mapPartition function by passing a store config.
So it must be serializable, but now it is not (for its membership flink env)

Either make ExecutionEnvironment in GradoopFlinkConfig transient or just remove extend relationship between GradoopFlinkConfig and GradoopStoreConfig.

A store instance is now independent from flink env, I vote the second.

[chpengzh]

Thus the creation of a store based DataSource will be like this:

 public HBaseDataSource(
    @Nonnull GradoopFlinkConfig flinkConfig,
    @Nonnull HBaseEPGMStore epgmStore
 )