Dynamic operations only pass valid params

[philippjfr]

When creating a Dynamic ElementOperation with streams sometimes you want to supply additional streams, which do not supply parameters to the operation. This ensures that Dynamic only passes along parameters that are accepted by the operation.

[jlstevens]

Looks fine and the change makes sense. I still don't quite get the motivation though:

When creating a Dynamic ElementOperation with streams sometimes you want to supply additional streams, which do not supply parameters to the operation.

What do you mean? Do you have an example? That said, I see how this change would make using streams more robust....

[philippjfr]

By default an operation can supply streams classes which supply parameters for the operation, e.g. think RangeXY which supplies x_range and y_range for the datashader operation. The user can however supply additional streams, which don't supply operation parameters, so this let's you do this:

bounds = Bounds(bounds=None)
decimate(datapoints, streams=[bounds, RangeXY()])

Without getting a bunch of warnings about bounds being passed to the decimate operation.

[jlstevens]

Ok. Makes sense and the tests are passing. Merging.