As the ordering of the random numbers within a multi-field are dependent
on the ordering of the keys, it is highly relevant even for the average
nifty user that keys are sorted. Hence, state so in the docstrings of
MultiDomain, MultiField and in the `from_random` method in sugar.py.

Adapt the ScalingOperator class to not depend on sugar.py in order to
use it within sugar.py without getting a circular dependency.

Make the ScalingOperator consistent with `from_global_data`, `full` and
possibly other operators which take the domain as first argument. This
breaks the currently enforced consistency with the `DiagonalOperator`
which takes a field as first argument and the domain only as an optional
keyword argument.

Fixes #279.

Reviewed docs on operators, library, sugar. Fixed bug in makeOp due to the recent BlochdiagonalOperator interface change