Allow text highlighting in Google Book Preview

[Dansoftowner]

In the Google Book Details panel it's impossible to highlight/select the description-text.
That's because currently the rendering is done by a MarkdownView (and because of that the HTML description needs be converted into markdown at the first step -> bad performance).

Suggestion:
Use a WebView to render the content. That's now possible because in JavaFX 18 it's possible to make it's background transparent.

Benefits:

• Improved performance (no need to convert html to markdown), can get rid of the jHtml2Md dependency
• The WebView allows to highlight selected text

Drawback(s):

• It will be harder to make the web-content synchronous with the Theme
  • Solution:
    • The WebEngine allows to set a user-stylesheet (containing web-css)
    • The Theme class should provide a web-view stylesheet (e.g by a getSimpleWebViewStylesheet(): String)