doc: Fix markdown format errors

Made the following minor changes:
* Fix broken links and point to correct image paths
* Remove dead links and references
* Fix table format to conform to Github Flavoured Markdown
* Add few common terms to glossary
* Maintain consistency of format in writing headings <h1..h6>
* Remove irrelevant files
* Remove references to contact Red Hat support.

Change-Id: I4aed4945d56b5d68b8ea133ce5fa3162bfc2864f
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/6514
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>