Embedding Prosody using AppImage:

Thanks to this commit, there is no more need to manually install Prosody
on the server.
The plugin now build and embed an AppImage of Prosody.

In this commit:
* building and using a Prosody AppImage.
* Adding a launcher in the AppImage: the first command argument tells if
  we want to run prosody or prosodyctl
* prosodyCtl functions now uses the AppImage.
* Prosody AppImage: extract once at the startup, then run the squashfs

server/lib/prosody/config/paths.ts

@@ -7,6 +7,11 @@ interface ProsodyFilePaths {
   data: string
   modules: string
   avatars: string
+  exec: string
+  execArgs: string[]
+  execCtl: string
+  execCtlArgs: string[]
+  appImageToExtract?: string
 }
 
 export {