Change gitignore to ignore solr, add Explanation nesting to Subject
Add Procfile to manage Solr in multiple Rails environments (dev, test)
Make sources many-to-many
Make IssueAreas and Indicators many to many, not polymorphic. It became apparent that we only needed to tag Indicators, so it didn't need to be polymorphic. Also added a line to each spec to ensure the subject is valid. There were some hangups there in testing.
Pull in gitignore from 'many' branch to avoid committing more solr data
Merge branch 'many' into develop
Fix nil explanation in subject view