Transparent background + fix

* Builtin Prosody, Share chat url: option to have a transparent background (for streaming integration).
* Builtin Prosody, Share chat url: fixed new day hidding when no scrollbar in readonly mode.

languages/eu.json

@@ -7,6 +7,7 @@
   "Share chat link": false,
   "Read-only": false,
   "Show the scrollbar": false,
+  "Transparent background (for stream integration, with OBS for example)": false,
   "Tips for streamers: To add the chat to your OBS, generate a read-only link and use it as a browser source.": false,
   "Copy": false,
   "Link copied": false,