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

build-prosody.sh

@@ -0,0 +1,54 @@
+#!/bin/bash
+
+set -euo pipefail
+set -x
+
+rootdir="$(pwd)"
+prosody_build_dir="$rootdir/build/prosody"
+prosody_destination_dir="$rootdir/dist/server/prosody"
+
+if [[ ! -d "$prosody_build_dir" ]]; then
+  mkdir -p "$prosody_build_dir"
+fi
+
+cd "$prosody_build_dir"
+
+if [ -f "$prosody_build_dir/livechat-prosody-x86_64.AppImage" ]; then
+  echo "Prosody image already built."
+else
+  echo "Prosody image must be build..."
+
+  # Prerequisite: you must have python3-venv installed on your system
+  if [[ ! -d "venv" ]]; then
+    echo "Creating the python venv..."
+    python3 -m venv venv
+  fi
+
+  echo "Activating the python venv..."
+  source venv/bin/activate
+
+  echo "Installing appimage-builder..."
+  pip3 install appimage-builder
+
+  echo "Copying appimage source files..."
+  cp "$rootdir/prosody/appimage_x86_64.yml" "$prosody_build_dir/appimage_x86_64.yml"
+  cp "$rootdir/prosody/launcher.lua" "$prosody_build_dir/launcher.lua"
+
+  echo "Building Prosody..."
+  appimage-builder --recipe "$prosody_build_dir/appimage_x86_64.yml"
+fi
+
+echo "Copying Prosody dist files..."
+mkdir -p "$prosody_destination_dir" && cp $prosody_build_dir/livechat-prosody-x86_64.AppImage "$prosody_destination_dir/"
+
+# For some obscur reason, if we keep AppDir and appimage-build folders,
+# and if we try to install the plugin using the Peertube CLI,
+# the installation fails because there are some subfolders that are right protected.
+# To avoid that, we clean them:
+echo "Cleaning build folders..."
+rm -rf "$prosody_build_dir/AppDir"
+rm -rf "$prosody_build_dir/appimage-build"
+
+echo "Prosody AppImage OK."
+
+exit 0