Require babl version 0.1.11

Which contains the correct RGB -> Y conversions.
operations,opencl: Follow up on the changes for babl Y conversions.

See d3e75895a994fa87640cf04c27314b1ff935675c in babl.
tests: Modify composition references for changed babl Y conversions.

See d3e75895a994fa87640cf04c27314b1ff935675c in babl.

Conflicts:
	tests/compositions/reference/softglow.png