[ReOpen] Enable Docker image to run TShock server as a non-root user

[kblaschke]

Running a game server as root is fine on a local machine, but on a public server, this might be a security issue. Docker supports the -u parameter, but with the current image, this just won't work because TShock creates a ServerLog.txt file in the /tshock directory. This fails because the directory is not writable to other users.

See pull request #16 for a possible fix.

[SharkWipf]

I know this is an ancient issue, but since I just ran into this, others might as well:
This PR does not 100% allow running as a different -user/group, for some reason the server crashes out without error when trying to generate a new world when not running as root.
Generating a world as root and then switching to user mode (after chowning the files) works fine, so I assume the server tries to create a temp file while generating the world.
It probably needs another symlink, if I can figure out where I might dive into it when I have more time.

[ryansheehan]

I know this issue is quite old. I just recently tried to build everything and internally to the container run under non-root privilege. TShock crashed however. I removed the non-root user and everything ran. PR's are welcome on this issue.

[ryansheehan]

Had to revert the non-root changes, was running into issues when the terraria user tried to write to a volume