Installation Quick Start Section (CDAP-695)

• Add an installation quick-start section. (Fixes https://issues.cask.co/browse/CDAP-695)
Staged: http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/admin-manual/installation/quick-start.html
• Add to installation index page.
Staged: http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/admin-manual/index.html
• Re-arrange installation guide to flow better.
• Improve progress messages from build script.
• Add "Removing an Application" to the getting-started section.

Staged at: http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/admin-manual/index.html

There may be additional cdap-site.xml properties that need flagging for the quick-start guide. If you know of any, please suggest in the comments.
also wierd that it links back to the full install guide, even though the full configuration section is included below.  Can/Should it just link to further down the quick-install guide?