Revive HsCesium for version 14

[jmacura]

Description

More effort is needed. HsCesium currently does not compile due to gazillion of "... 'rootDir' is expected to contain all source files" errors. Probably Project References may help here, but I did not succeed in this matter yet. Any help appreciated.

Related:

• https://stackoverflow.com/questions/57422458/error-ts6059-file-is-not-under-rootdir-rootdir-is-expected-to-contain-al
• https://stackoverflow.com/questions/55753163/package-json-is-not-under-rootdir/61467483#61467483

UPDATE:
The problem was simply in the fact that hslayers lib was not compiled beforehand. Project references might solve that, but I fail to implement them, hence I keep the "path" way to link hslayers and hslayers-cesium for now.

TODO:

• move 3D view toggle button somewhere else (toolbar?)
• differentiate 3D view toggle button when 3D on/off

Related issues or pull requests

fixes #4048
fixes #4750
port of #4751

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Dependency updates
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe)
• I am unsure (we'll look into it together)

Do you introduce a breaking change?

• Yes
• No
• I am unsure (no worries, we'll find out)

Checklist

• I understand and agree that the changes in this PR will be licensed under the [MIT License]
• I have followed the guidelines for contributing
• The proposed change fits to the content of the code of conduct
• I have added or updated tests and documentation, and the test suite passes (run npm test locally)
• I'm lost; why do I have to check so many boxes? Please help!

[jmacura]

Adds testing files to cesium-test-app for GeoJSON source and KML source.

Moves Cesium/OL 3D/2D toggle button from sidebar to toolbar. The background colour indicates the 3D view is active.
Before:
After:

[jmacura]

After incorporating the latest changes from develop, the toolbar actually looks like