[FLINK-1178] Changed type preference to ValueType, WritableType, CaseClassType

This closes #162
Remove unnecessary final modifier in PlanExecutor.loadExecutorClass method

Remove unnecessary final modifier in PlanExecutor.loadExecutorClass private static method because private means you can not override this method.

Author: Henry Saputra <henry.saputra@gmail.com>

Closes #163 from hsaputra/remove_unneeded_final_privatetatsic_planexecutor and squashes the following commits:

fe7afc7 [Henry Saputra] Remove unnecessary final modifier in PlanExecutor's private static method.
[FLINK-1194] Fix Java quickstart archetype POM file

This closes #165
Add DeltaPageRank example
[FLINK-1182] Improve error messages for POJO type mismatches
[FLINK-1181] Fix IOReadableWritable checks in RPC service

This closes #167
[FLINK-1174] [streaming] Added window join operator