Host injected CSS eternally instead of in the app

[ThijmenDam]

Currently the injected CSS (i.e. the CSS to adapt the Google / DeepL translate page to suit the small window) is embedded in the source code of BarTranslate. This means that whenever Google or DeepL updates their translate page layout, users have to install a new version of BarTranslate to get the updated CSS. This problem can be circumvented if the injected CSS is hosted elsewhere, so that I (or other contributors) can adapt this CSS on the fly.