syskit: allow to selectively disable the startup of the transformer broadcaster

Its availability is not needed for syskit to work properly, and in
some cases it is useful to get it started externally by e.g. scripts
bugfix: allow multiple callbacks on transformation elements

Having only one callback broke the register callback functionality
on the Transformation object in case that two transformation objects
shared one transformation elemtent
syskit: fix behaviour when a placeholder task ends up being a transform producer
syskit: fallback to the full task if the selected data service has no transformation output port

One thing that one definitely wants to do in the syskit transformer
configuration is use devices or definitions as e.g.

  dynamic_transformation one_dev, 'bla' => 'blo'
  dynamic_transformation one_def, 'bla' => 'blo'

The issue is that the device or definition might be a data service
(i.e. not the full task) and therefore will not have the
transformation output of the full task.

The sucky part of this change is that it is NOT guaranteed
that ANY device driver for a particular device provides a
transformation producer, which means that changing the device
driver might make the transformer resolution go boom. However,
this is such a usability issue that I prefer this corner case
to fail.
Merge remote-tracking branch 'autobuild/next'
bugfix: Implement addTransformationChangedCallback not setTransformationChangedCallback

There was a wrong name in a overwritten virtual method
Bugfix: Do not register updateCallbacks several times

There was a bug, that on every discovery of a new transformation
the callback for a transformation was re-registered.
swap frame names when creating inverse transform
Add time stamp to static transforms
Merge branch 'master' of ssh://aila-control/home/sempromuser/RockDev/drivers/transformer
Bugfix: Also call update callbacks for static only Transformations

In case, that a transformation was only represented by static elements,
the update callback was never called. This issue is fixed with this commit.
syskit: better debug output
syskit: update w.r.t. split of validate_* flags in engine
syskit: fix transformer configuration inheritance across profiles