Toolbar dividers

[kecnry]

Description

This pull request adds vertical dividers and padding to the app toolbar to clearly differentiate between different "tools" (and as a bonus, fixes the layout of the redshift select element to be vertically centered). Some vertical dividers already existed, but they were applied inconsistently. See before and after screenshots below.

Before:

After:

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 change log needed? If yes, is it added to CHANGES.rst?
• Is a milestone set? Milestone is only currently required for PRs related to Imviz MVP.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)?

[codecov]

Codecov Report

Merging #944 (1366710) into main (3dbc20f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #944   +/-   ##
=======================================
  Coverage   69.40%   69.40%           
=======================================
  Files          69       69           
  Lines        4880     4880           
=======================================
  Hits         3387     3387           
  Misses       1493     1493           

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[pllim]

I pinged PO on Slack to review this. FYI.

[rosteen]

Looks good to me!

[PatrickOgle]

Looks Good. Thanks.