Cleaning up global properties / settings
This cleans up handling of settings proxies and global-properties-proxies such as the "ColorPalette" proxy. The two concepts were fairly similar and hence we merge them. vtkSMGlobalPropertiesProxy no longer exists instead the role is taken up vtkSMSettingsProxy.
Links setup with vtkSMSettingsProxy are now serialized in the state files and thus can be restored correctly (fixes #16864 (closed)).
Property hints for specifying links with settings and color palette are now unified.
Also avoid custom filter definition creep. Fixes #19340 (closed)