Re-enable 30 and 365 day insights for likes, faves and reshares

Added InsightBaselineDAO::doesInsightBaselineExistBefore and Implementation
Added "sharing" to InsightTerms.
Created test for favelikespike
Created test for retweetlikespike
Some refactoring of repeated code

@ginatrapani - One question I had, was, is checking for an existing baseline what I should do?  Or should  I have them all just add a generic, "this insight ran today" baseline.  Or... do we have one of those already?  (Referencing lines 40-50 of webapp/plugins/insightsgenerator/insights/favlikespike.php, for example)