[RocksJava] GetIntProperty in RocksDB

Expose GetIntProperty methods to RocksJava. As the integer(64-Bit)
value is no integer in Java the method is aligned with the return
type which is long.
[RocksJava] Improved comments in RocksDB class

Improved comments in RocksDB getLongProperty methods,
to describe the behavior more detailed.
Merge pull request #397 from fyrz/RocksJava-GetIntProperty

[RocksJava] GetIntProperty in RocksDB