fix footprint defaults when changing traitlets before plugin active

[kecnry]

Description

This pull request fixes respecting user-changed traitlets (specifically color, but also applies to the preset selection) when those traitlets were set in the API before the overlay objects are fully initialized when the plugin is first opened.

See the included regression test or the following example:

fp = imviz.plugins['Footprints']
fp._obj.vue_link_by_wcs()
fp.color = '#ff33ff'
fp.open_in_tray()

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Patch coverage is 66.66% of modified lines.

Files Changed	Coverage
...nfigs/default/plugins/plot_options/plot_options.py	39.13%
...viz/configs/imviz/plugins/footprints/footprints.py	90.90%
jdaviz/configs/imviz/tests/test_footprints.py	100.00%

📢 Thoughts on this report? Let us know!.

[pllim]

Thanks!

[camipacifici]

Fixes the problem, thank you!

[kecnry]

Setting back to draft while I look into the issue of overwriting an existing regions object (that used to work - there is a chance this broke that, so I want to make sure it didn't and make sure we have test coverage for that case).

[javerbukh]

Fixes the bug as described, thanks!