Add diagnostic info for connection pools to Help page

Backend changes:
Add org.clojure/java.jmx dependency to project.clj for use in JMX bean querying
To troubleshooting.clj, add some functions to capture details from the c3p0 connection pool beans to a map
Add new API endpoint to invoke that from util.clj
Add content-disposition header to API endpoint to make it a download

Frontend changes:
In the Help page, add a new paragraph below the existing "Diagnostic Info" JSON blob for advanced details, envisioned as a list of download links (which users can then attach to tickets, etc.)