Graphs that were using `file_exists()` to check for the presence of RRD
files now use `rrdtool_check_rrd_exists()` instead. This is a fix for
distributed poller configurations that are running `rrdcached` on a
different host.
- UDP Jitter metrics collected.
- Added opstatus code and DB field
- Discovery sets opstatus
- Added Status selector to SLA page
- Merged master and moved SQL