Add Namespace and/or MAC profile for gngr browser

Namespaces and Mandatory Access Control are great sandboxing features within Linux, would be nice to consider supporting them e.g: 

Namespaces: [Firejail](https://firejail.wordpress.com/)

MAC: [Apparmor](https://apparmor.net/)

(Apparmor comes by default enabled within Debian 10+, Firejail is installable from stable repos)
