Nicer captions / updated text&screenshots

[alessandrofelder]

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Description

What is this PR

• Bug fix
• Addition of a new feature
• Other

Why is this PR needed?

• We've changed the title of structure view widget in brainrender-napari from "3D brain region meshes" to "3D atlas region meshes".
• There is a bug in the captions display: Captions are on the wrong line.

What does this PR do?

• fixes captions and updates text and screenshots with name change.

References

Closes #58
Closes #60

How has this PR been tested?

Visual inspection (I could reproduce #60 before these changes).

Is this a breaking change?

No

Does this PR require an update to the documentation?

No

Checklist:

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