CC-5860: Analyzer HTTP requests can hang indefinitely

* Log a backtrace when sent the USR2 signal (kill -SIGUSR2 <pid>)
* Rigged up up something to strace and restart when we see a request hanging
Merge branch 'cc-5709-airtime-analyzer' of github.com:sourcefabric/Airtime into cc-5709-airtime-analyzer
CC-5862: Invalid UTF-8 chars cause DB error

* Strip and validate UTF-8 strings in the Media API
* Also properly parse track numbers containing "-"