Allow enabling Finder Scope inside of pywwt

[Carifio24]

Overview

With the Finder Scope now embedded in the research app in WorldWideTelescope/wwt-webgl-engine#324 (and subsequent PRs), this PR adds the ability to turn the Finder Scope on from inside pywwt.

The changes are as follows:

• Add a finder_scope_active traitlet to the WWT widget that controls whether the scope is active or not. This passes a message to the research app to control the relevant setting there
• Add a finder_scope_place property to the widget that gives the current value under the Finder Scope as a wwt_data_formats.place.Place. If there isn't one, this value is None
• We allow setting a callback to be executed every time the selected Finder Scope Place changes. This method is chosen for consistency with what we do for source selection.

TODO: Need to add a test

Checklist

• Changed code has some test coverage (or justify why not)
• Changes in functionality documented (or justify why not)

[Carifio24]

Rebase for some CI updates.

[Carifio24]

Rebased to pick up CI updates