bug 826564 Add exploitability to reports_clean
Backill and update functions for exploitability

* Add crontabber jobs for matview
* Add backfill and update functions for daily exploitability rollup
Fixed minor typo in installation docs.
Merge pull request #1277 from selenamarie/bug826564-exploitability-sql

bug 826564 Add exploitability to reports_clean
Merge branch 'master' into bug819426-exploitable-crash-bugs-report