HistoSys and OverallSys with shared nuisance parameters are not supported

[lukasheinrich]

Description

In the case we added here #272 roohf allows multiple modifiers of different type to share the same nuisance paramerers. We need to support this, and in principle it's is not a big issue. For it we need to

• decouple constraint pdfs from modifiers
• deprecate qualify_names

similar to how samples can subscribe to modifiers and many samples can hook into the same modifier, modifiers can subscribe to constraint terms, where many modifiers hook into the same constraint terms.

Some checking needs to occur because not all modifiers can work with all constraint terms

[kratsg]

Also additionally deprecate qualify_names as well.

[kratsg]

Done with #354 and #358.