Save files should record the server and dimension that they describe

[totemo]

There are a few parts to this:

• The file name should probably name the server and maybe the world name.
• The file filters could filter out saves that don't apply to the current server.
• Saves MUST load into the server and dimension that they were created from, and no other.
• The save file contents should probably also include a header that names the server and dimension on the first line of the file in the form: @server/worldname, since the file name can be any arbitrary string.