Swap order of arguments of ScalingOperator

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.
9 jobs for nifty6_scalingoperator_arg_order in 8 minutes and 54 seconds (queued for 1 second)
Status Name Job ID Coverage
  Build Docker
passed build_docker_from_cache #978741

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  Test
passed test_mpi #978743

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passed test_serial #978742

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  Demo Runs
passed run_bernoulli #978748

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passed run_curve_fitting #978749

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passed run_getting_started_1 #978745

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passed run_getting_started_2 #978746

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passed run_getting_started_3 #978747

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passed run_ipynb #978744

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