CMS: update about CMS page

[katilp]

Update "About CMS" page: http://opendata.cern.ch/docs/about-cms

• Update the 2 links (both broken) in "information about the CMS detector design and overview" -> https://cms.cern/detector
• Update Guide to research use of CMS Open Data. to CMS open data guide https://cms-opendata-guide.web.cern.ch/
• Update the link to the object pages to 2015
• Update VM link cms-virtual-machine-2015
• Rename "An analysis example chain," to something else, the new getting started is not a chain, and update the link to cms-getting-started-2015
• Update MiniAOD/MiniAODSIM text to reflect 2015 release
• Update how to join to https://cms.cern/collaboration/how-join-cms
• Update "Other CMS open data" links for publications and HEPData
• update policy to http://opendata.cern.ch/record/415