Rework 4D tools so that they do not depend on ComputationUI anymore

[Brow71189]

All tools in here: https://github.com/nion-software/experimental/tree/master/nionswift_plugin/nion_experimental_4dtools

They use very old code that is hard to maintain and we get frequent bug reports about it from users.

• Most importantly, we need to remove the dependency on ComputationUI because that was a hack implemented before we had a proper way for defining custom UI in computations.

• Also these tools should use these functions: https://github.com/nion-software/niondata/blob/master/nion/data/MultiDimensionalProcessing.py as much as possible for the actual data processing part.

• Finally we should think about removing computations that are not needed anymore. As far as I can tell we do not need the special dark subtracion routines anymore, so I'd like to remove those instead of reworking them

• Think about a better menu structure for our "experimental" tools: I'm not very happy with how they are spread across different menus. Some items are prefixed with [EXPERIMENTAL] in their title, some aren't. Maybe we could have one "experimental" menu item where all the experimental tools go. Once we merge one into stable they will move out of the experimental menu but there should be a note that this tool was moved for at least one release.

[cmeyer]

Reference:

• Computations should have the ability to do partial updates. nionswift#1014

[cmeyer]

Superseding issue:

• Extend edit computation with new features to replace nionswift-experimental Computation panel nionswift#1096