new paths are now defined in _common.sh like this
```
flohmarkt_install="/opt/${id}/${domain}${url_path}/src"
flohmarkt_venv_dir="/opt/${id}/${domain}${url_path}/venv"
```
giving a nice layout following the domain and path the flohmarkt uses as its URL.
Activated path resource in manifest.toml to let the admin choose a path different from '/'.