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.
• Added documentation for https://issues.cask.co/browse/CDAP-663, "Getting a Health Check".
• Added docs on rehiring path parameters to be percent-encoded (https://issues.cask.co/browse/CDAP-728); see staging at:
- http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/reference-manual/http-restful-api/introduction.html#reserved-and-unsafe-characters, 
- http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/developers-manual/building-blocks/services.html#service-handlers, 
- http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/reference-manual/http-restful-api/service.html#requesting-service-methods

• Modified property descriptions of the cdap-site.xml file (https://issues.cask.co/browse/CDAP-454); staged at:
- http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/admin-manual/installation/cdap-site.html#appendix-cdap-site-xml
- http://stg-web101.sw.joyent.continuuity.net/cdap/2.6.0-SNAPSHOT-2.6.0_doc_updates/en/admin-manual/installation/installation.html#configuration

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.
Weird to use "we" in this sort of doc. Maybe `For upgrading existing CDAP installations, read the :ref:Upgrade Guide <install-upgrade>`