[RocksJava] Memtables update to 3.6

- Adjusted HashLinkedList to 3.6.0
- Adjusted SkipList to 3.6.0
- Introduced a memtable test
Merge pull request #354 from fyrz/RocksJava-memtables-3.6

[RocksJava] Memtables update to 3.6