Edit axis labels

[DanicaSTFC]

Describe your changes

• Added method to edit labels of the axes in the viewer base class
• Edited the key press event so that x y z are hidden on the 2D view when the orientation is changed
• Added unit test for method edit the labels

Note: this PR does NOT add unit test for the interactor (changes in Wrappers/Python/ccpi/viewer/CILViewer2D.py). The x, y, z pressing and label editing should be added in a new PR.

Describe any testing you have performed

Consider adding example code to examples

• pip installed and added arbitrary labels in the main window
• pressed x y z to see the changes in the labels. noticed and opened this issue axis flicker #392
• run all unit test (one failing failing unit test: pytest and QApplication #367)
• written unit test for setting the labels
• not tested on the web viewer, see Web viewers errors #400

Link relevant issues

Partially closes #122. Long text in the labels would still be not formatted well. Opened #398

Checklist when you are ready to request a review

• I have performed a self-review of my code
• I have added docstrings in line with the guidance in the CIL developer guide
• I have implemented unit tests that cover any new or modified functionality
• CHANGELOG.md has been updated with any functionality change
• Request review from all relevant developers
• Change pull request label to 'waiting for review'

Contribution Notes

• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CILViewer (the Work) under the terms and conditions of the Apache-2.0 License
• I confirm that the contribution does not violate any intellectual property rights of third parties

Qt contributions should follow Qt naming conventions i.e. camelCase method names.

VTK contributions should follow VTK naming conventions i.e. PascalCase method names.