This commit introduces a resume capability for the
dispute coordinator subsystem. Specifically, this will allow
to recover data for disputes for which we have no local statements.

… Harness

This commit modifies the TestHarness to return a TestState. We subsequently
define a resume function on TestState that allows to interrupt the test and
test specifically for behavior on startup of the subsystem.

This commit implements the resume functionality for the subsystem.
In addition, we will forward any DisputeParticipation::Participate
message in order to ensure that disputes for which we do not have
local statements may be recovered in due time.

handle local_statements that are not missing.