padManager padList cache is never refreshed

[s1341]

The padList cache implemented in db/PadManager.js is never refreshed, so requests for e.g. listAllPads() will only ever return the list generated the first time the padManager is used. There should be a mechanism to refresh the cache.

[s1341]

This is a duplicate of the bug fixed in pr #1974. I hadn't updated my base to the head ;)