Support generic Hadoop Compatible Filesystem

This is a shortened version of PR #358, with focus on filesystem only.
Tachyon supports more and more different under filesystems. It makes more sense to create a page like "configure under filesystem", which contains links to configure HDFS, S3, Glusterfs, Ceph etc. Also add a page about how to add more under filesystems for other systems to integrate.

This page is fine for this PR. Please create another JIRA for this documentation task. Thanks.