Added style guide to documentation. Updated buildinsight with link to
style guide.
Added percent symbol to alternate text for AgeAnalysis.
Merge pull request #2160 from cdmoyer/add-percent-symbol-to-age-analysis

Age analysis insight fix: Add percent symbol to alternate text
Add InsightPluginParent::shouldGenerateAnnualInsight
Add InsightPluginParent::shouldGenerateEndOfYearAnnualInsight
Added getThisYearOfPostsIterator to PostDAO
New insight: Thanksgiving Who You Thanked insight
Staging: Test Thanksgiving Who You Thanked insight on Nov 21st