Allow persistent data for container

[m1k1o]

This PR is adding functionality to mount folders to containers. User's path root will be changed to custom container folder in instance data folder: <instance.data>/<container.name>/<users.path>.

To do

• When folder does not exist, it creates with root:root user, and is not accessible for neko user inside container.
  • Switched to mounts instead of binds, target folder must exist now. (changed in 0e99dd5)
• Path root can be bypassed easily with adding /../ to path. (fixed in 1345118)

[m1k1o]

Should mount /data folder to neko-rooms and create new folder before mounting. That would need two paths for data:

• one inside cointainer
• another on the host

They need to match, otherwise it won't work.

[m1k1o]

Neko rooms is running as root (even if only inside container), although it does not need to. And creatilg file results again to a file owned by root.

[m1k1o]

There should be posibility to add readonly template files from a shared directory, rather that having everything split per rooms. And additionaly allow whitelisted external mounts (for downloads folder, or media...).

[m1k1o]

Maybe neko-rooms could copy its data mountpoint information (since it has access to docker socket) and use that, instead of setting another external env variable. Update: Needs refactoring, new PR.