Metric board configuration files should be managed by the server backend, too.

[koschke]

The configuration parameters for metric boards are saved by our ConfigIO framework analogously to AbstractSEECity classes. They currently have the same file extension .cfg. Our server backend uploads all files with this file extension, but then chooses one of these randomly to configure a code city. If it picks a file meant to configure a metric board, it will run into problems.

The configuration files for metric boards should have a different file extension .mbc (for metric board configuration). Those file need to be uploaded and used by the server backend server, too.