Load PeerFinder database in Stoppable::onPrepare:
OverlayImpl::onStart calls into PeerFinder before PeerFinder::Manager::onStart,
causing tests to sometimes fail and the application to intermittently not start.
The order of calls to Stoppable::onStart is implementation defined and not
predictable.

This changes PeerFinder to load the database in Stoppable::onPrepare, before
threads are launched. In general, creation and initialization of resources that
are shared between classes should happen in onPrepare rather than onStart,
to solve this problem.
Keep a list of section config values that are not key/value pairs:
This change to BasicConfig stores all appended lines which are not key/value
pairs in a separate values vector which can be retrieved later. This is to
support sections containing both key/value pairs and a list of values.
Add doors section in cfg
Add MultiDoor
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