Feature/service loader

Integrates TFS with Hadoop 2.x's ServiceLoadering of FileSystem types.

The core idea of this patch is to make it that users don't need to modify the hadoop config files in order to use tachyon.  Hadoop 2.x introduced ServiceLoading of FileSystems based off a FileSystem.getScheme method.  This patch splits the two different schemes into two different classes and adds ServiceLoading support.  This patch will not have any effect on Hadoop 1.x, so the only change for 1.x programs is that tachyon-ft is now a different class.

This patch is not done yet, still need to do more testing, but sending early to get feedback.
Let's add Apache license header since Tachyon also distribute the source code.