Allow for a reactor to be loaded without setting its cs to the master

[keckler]

Description

When loading a reactor from a DB, it has been the default behavior to apply the associated CS to be the "master" CS for the run. This is not always desirable. Just because you load a reactor doesn't mean you want to apply it to the entire run. This small PR simply allows for that possibility.

This is related, but not actively working against, #930 .

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[john-science]

I'm okay with this. But:

1. I will have to remember to remove this when I remove getMasterCs() and setMasterCs(). Though, I will be fairly busy until Halloween, so sure.
2. Since this feature is being removed, I'm not sure we need the release notes.

[keckler]

Yeah, its in the checklist for #930 already. So should be good to go wrt remembering.