Fix NPE originating in FactionAccountHolder

Help id.startsWith("faction-") realize its truthiness.
(Todo: Convert/clean up old Factions DB records.)
Sketchy chest location for attached signs

Locate chests with attached signs; and fail if no valid containers are
found. Could use a good refactoring.
Merge pull request #55 from bezeek/upstream

Fix NPE originating in FactionAccountHolder; fix attached signs