Simplify native library resolution using os-maven-plugin

Motivation:

So far, we used a very simple platform string such as linux64 and
linux32.  However, this is far from perfection because it does not
include anything about the CPU architecture.

Also, the current build tries to put multiple versions of .so files into
a single JAR.  This doesn't work very well when we have to ship for many
different platforms.  Think about shipping .so/.dynlib files for both
Linux and Mac OS X.

Modification:

- Use os-maven-plugin as an extension to determine the current OS and
  CPU architecture reliable at build time
- Use Maven classifier instead of trying to put all shared libraries
  into a single JAR
- NativeLibraryLoader does not guess the OS and bit mode anymore and it
  always looks for the same location regardless of platform, because the
  Maven classifier does the job instead.

Result:

Better scalable native library deployment and retrieval