Make conf directory mappable

[bnhf]

Seems like a good plan to me to make the conf directory mappable (through volume binding in Docker). This would allow advanced users to edit the app.conf (Beego web framework config file), and the template files that are used to create OpenVPN client files, at the host level (by command line editors, Cockpit with the Navigator addon, or Webmin for example).

We'd check for the existence of these files at container start, and if they don't exist (e.g. mapped for the first time), we'd copy them from a default directory.

[palzino]

would this feature enable the usage of multiple different subnets instead of a single one?