CLC-1220 Automating downgrades as well as upgrades

JIRA: https://jira.media.berkeley.edu/jira/browse/CLC-1220

These changes let us automate the downgrade process. The code now knows the db version of the previous release. Because of the way Rails migrations work you run the downgrade on the code you are downgrading FROM, then you git checkout the previous version and start trinidad. 

Once this is accepted into master I'll issue another PR for QA.