MySQL: implement incremental truncation and backup

As a developer i would like to spend less time truncating databases. While there are other longer term solutions being looked at, something like the following may work in the intermediate:

- mysql instance on central (windows or otherwise) server, will host per instrument databases called `archive_ndxzoom` etc.
- run scheduled daily task python script on each NDX that
- backs up data that is both (a) not yet saved in a nexus run file and (b) older than a certain time threshold to both stage deleted sql files and the central mysql `archive_ndx*` table
- if both above successful, deletes these rows from local NDX database
- ibex client could by default look at central mysql as well as local mysql (just adding an extra url to a plugin.ini) but need to check performance of this as a default