[Java] Fixed link error on library loading on Mac.

Summary:
Fixed link error on library loading on Mac.

Test Plan:
make rocksdbjava
make jtest
[Java] Fix compile error on DbBenchmark.java

Summary:
Fix compile error on DbBenchmark.java

Test Plan:
make rocksdbjava
make jdb_bench
Column family support in RocksJava

This commit includes the support for the following functionalities:
  - Single Get/Put operations
  - WriteBatch operations
  - Single iterator functionality
  - Open database with column families
  - Create column family
  - Drop column family
  - Properties of column families
  - Listing of column families

In addition there is an additional Java sample which can be build
using "make cfsample".

What is not supported currently using RocksJava:
  - Multi Iterator support
  - MultiGet

I decided to file a pull request w/o the missing two features to omit
some merging trouble. I would propose to hand them over to a later point
of time.
Quality improvements
- Replaced all NULL occurences in code with nullptr
- Removed iostream include
Fixed some lint problems
More lint problems fixed
Moved Testing code from Sample to Test.
Fixed line length in Test