Discussion: _counters_tree() to be used to build any kind of scan chains
Description:
_counters_tree function in common/scans.py is used to build the
default scan chain -- it would be good to be able to use it for
scans in general, like the shutter characterisation scan from ID11 ;
in this case two p201 counters are added in an integrating acq device,
and the _counters_tree function or equivalent would simplify this
provided that it is made more flexible (with the possibility of
giving a known master for the counters instead of having a default
one)