Fix Albumik frontend assets and YunoHost upgrade scripts

scripts/upgrade

@@ -1,11 +1,14 @@
 #!/bin/bash
 set -euo pipefail
-source ./_common.sh
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+source "$SCRIPT_DIR/_common.sh"
 
 app="${YNH_APP_INSTANCE_NAME:-albumik}"
 
 mkdir -p "$install_dir"
 
+rm -rf "$install_dir/backend" "$install_dir/web" "$install_dir/doc"
+
 cp -a "$YNH_APP_BASEDIR/backend" "$YNH_APP_BASEDIR/web" "$YNH_APP_BASEDIR/doc" "$install_dir"/
 
 chown -R "$app:$app" "$install_dir"
@@ -15,3 +18,5 @@ systemctl restart "$app"
 
 nginx -t
 systemctl reload nginx
+
+echo "Albumik upgraded"