feat: added automatic import of cesium css

[jfayot]

This is a proposal to add Cesium css (Viewer's as well as CesiumWidget's) automatically by the plugin.
This allows to get rid of imports in code.
Not done yet, but this could be deactivated by an additional option if you think it's better.

[jfayot]

I just realized I forgot to update the REAME...

[jfayot]

I'll let you update the Chineese version if you accept this PR...

[s3xysteak]

Looks good to me but I think it will break apps using Cesium version 1.96 and earlier. Could you add an option css, which defaults to false, and enable this feature by setting it to true?

plugins: [
  cesium({
    css: true
  })
]

So that I can release it as a patch. We can pick a good day to release a minor version which using css: true as the default.

[jfayot]

You're right ! Done

[jfayot]

In the meantime, I've reverted the examples. We shall update them when defaulting css to true ?

[s3xysteak]

I can update them when needed. Thanks for your contribution! I think it will be released in a few days.

[s3xysteak]

I think it has been ready to be merged. If you have any more issues plz remind me! It will be merged and released tomorrow.