Port sources to also use the host services infrastructure that is
used by inputs, devices and mounts. Sources are a bit different
from the other services that they don't run for the duration of
the stage but are run before anything is built. By using the same
infrastructure we re-use the process management and inter process
communcation. Additionally, this will forward all messages from
sources to the existing monitoring framework.
Adapt all existing sources and tests.
Add a new source for transporting binary data within the source
entry itself. The data is ascii encoded in the `data` property
of the inline source item, with the encoding that is used being
specified in the `encoding` property.
