Overload operations on OutputPorts

It seems like it should be possible to do things like:

from b_asic.core_operations import Butterfly, Constant

bfly1 = Butterfly()
c = Constant(0.5)

bfly1.output(1) + c  # Works
bfly1.output(0) + 0.5  # Does not work

So similar operator overloading as for Operation should be implemented, probably on SignalSourceProvider.