menu: create volumes with current user

Most services won't explicitly create volumes/ -folder when added, hence
Docker will create volumes as owned by root. This will later cause
problems for build hooks trying to prepare directories.

E.g. adding nextcloud later will fail with:

    Error running PreBuildHook on 'nextcloud'
    [Errno 13] Permission denied: './volumes/nextcloud'

Creating volumes as part of the initial git-clone will ensure it's owned
by the correct user.

.gitignore

@@ -1,6 +1,5 @@
 #ignore data folders for containers
 /services/
-/volumes/
 /backups/
 /.tmp/*
 __pycache__

volumes/.gitignore

@@ -0,0 +1,3 @@
+# This file is needed for the volumes-folder to be created with the correct
+# ownership as part of the initial 'git clone'.
+*