Info message when running BrainGlobe Registration plugin with no atlas installed

[saarah815]

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Description

What is this PR

• [ ] Bug fix
• [x] Addition of a new feature
• [ ] Other

Why is this PR needed?

If user has no atlases installed, this widget informs user that they need to install atlas(es) before they are able to use BrainGlobe Registration plugin.

What does this PR do?

If no atlases installed:

• Info message in terminal: "No atlas installed. Please download atlas(es) from https://github.com/brainglobe/brainglobe-atlasapi"
• Message box appears in Napari GUI with same message

References

Please reference any existing issues/PRs that relate to this PR.

Issue #15

How has this PR been tested?

Please explain how any new code has been tested, and how you have ensured that no existing functionality has changed.

• No atlases downloaded - info messages appear as expected
• Atlases downloaded - info messages do not appear (as expected)
• Deleted all atlases - info messages appear as expected

Is this a breaking change?

If this PR breaks any existing functionality, please explain how and why.

N/A

Does this PR require an update to the documentation?

If any features have changed, or have been added. Please explain how the documentation has been updated (and link to the associated PR). See here for details.

N/A

Checklist:

• [x] The code has been tested locally
• [ ] Tests have been added to cover all new functionality (unit & integration)
• [ ] The documentation has been updated to reflect any changes
• [x] The code has been formatted with pre-commit

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 82.98%. Comparing base (538cdd2) to head (62b095a). Report is 1 commits behind head on dev.

Files	Patch %	Lines
brainglobe_registration/utils/utils.py	85.71%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #46 +/- ## ========================================== + Coverage 82.91% 82.98% +0.07% ========================================== Files 8 8 Lines 515 523 +8 ========================================== + Hits 427 434 +7 - Misses 88 89 +1 ```

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[IgorTatarnikov]

I just noticed that we have the display_info convenience function in brainglobe-utils.qtpy.dialog that takes care of the Qt internals. This can simplify the code even further, you can import it and just call display_info with the corresponding title and message if no atlases are installed!

[saarah815]

Last set of changes I promise! I'll mark it as approved, you can make the final changes and then I'll merge it in!

Perfect, thank you!