Layered FS for server istances

Currently, the process of creating a new server is basically a copy of server-template directory and some symlinking operations.

Symlinking has this drawback, that server instances need to have always the same set of files. No way of customizing, as the set of symlinks will be always the same.

If there was a layered / COW filesystem (lower layer for server base files, upper layer for server data) it would be easy to actually customize servers. Even having many server versions would be possible (many base layers for different server versions).

E.g. creating and activating a new server:

1. Create a new, clear upper layer
1. Copy server template files to this new upper layer
1. Stop the current server process
1. Unlink current upper layer from the server and attach the new server layer (activation)
1. Start the server
1. Win?