Import "manual testing" pages from wiki

Created by: seancolsen

This PR imports the following pages from the wiki into one MkDocs page:

• https://wiki.civicrm.org/confluence/display/CRMDOC/Manual+testing
• https://wiki.civicrm.org/confluence/display/CRMDOC/Dedupe+and+merge+testing
• https://wiki.civicrm.org/confluence/display/CRMDOC/Smart+group+testing
• https://wiki.civicrm.org/confluence/display/CRMDOC/Tarball+installation+testing

@stevekessler any interest in reviewing?

I'll merge on 2017-08-17 if no comments.