3109: Bumps v1.* compatibility fix

[krzywon]

Description

This circumvents the fitting issue related to the recent changes in the bumps package that require parameter values to be floats, where SasView has been using uncertanties objects. The Parameter object has an optional attribute called slot introduced in v1.* that I am using here instead. This attribute does not exist in v0.9.3 of bumps, but the way I am using it creates a new attribute of the parameter, maintaining backward compatibility.

Fixes #3109
Fixes #3227

How Has This Been Tested?

Tested locally using both bumps v0.9.3 and v1.0.0a10. Fits (and subsequent fits in the same tab) are successful for both versions of bumps.

Review Checklist:

Documentation (check at least one)

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• There is a chance this will affect the installers, if so
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)

Licencing (untick if necessary)

• The introduced changes comply with SasView license (BSD 3-Clause)

[jamescrake-merani]

Code looks fine to me, and works on my machine.