Incomplete severity levels levels and inconsistency between front and back end of application for advisors (Security)

Currently the advisors (Security right now) only support the following severity levels:
Notice
Warning
Error
and there are many more standard ones (Info comes to mind but there are more).  We should implement (and publish) what the accepted levels are for creating advisors and I'm guessing this should be mirrored in Alerting as well

Additionally, at least in Security Advisor the levels we do support are re-mapped on the front-end as:
Notice: Trivial
Warning: Major
Error: Critical 

which either needs to be documented somewhere or realigned somehow.  

How to test

All 8 severities should be usable now, on both Alerting and Advisor checks.