Add className prop to all layers

[ludvigeriksson]

The className prop was missing (defined as the first prop here: https://openlayers.org/en/latest/apidoc/module-ol_layer_Base-BaseLayer.html), so I added it to all layers.

[mmomtchev]

@ludvigeriksson this is missing unit tests

I switched to the official codecov action, you can try rebasing and it should start working for PRs

[ludvigeriksson]

@mmomtchev Will it be merged if I add unit tests? My previous PR (#277) didn't.

[mmomtchev]

If you add unit tests that cover the added code and all the unit tests work, yes it will get merged. If you insist on posting comments simultaneously with other persons involved in the extortion, it will still get merged, however I will say it loud and clear.

[ludvigeriksson]

This is the second time you have accused me of extortion when I'm trying to contribute to your open source project that you have chosen to publish. Since you clearly are not interested in driving this repo in a professional manner, I will continue working on my own fork instead. I wish you all the best in the future, and thank you for the ground you have laid in this project.