Re-import failed messages from error.log on a fresh db

If for some reason the user has deleted the RavenDB database and starting fresh and the user attempts to move messages from error.log back into the error queue for ServiceControl to rehydrate the error messages, in this case, we won't have a corresponding saga. Therefore we are using SingleOrDefault instead of Single.
Add a DB maintenance mode to ServiceControl

Added the-maintenance  command line switch to allow ServiceControl to be
started with reduced functionality.  In this mode it serves up the
RavenDB Web UI but disables the Raven Bundles and the periodic deletion
code and does not start the bus so message processing and the REST API
are also disabled.
Merge branch 'release-1.4.0'
Merge branch 'master' into develop