Add configuration options

[megabyte6]

Add a configuration file so options such as "backup interval" or "server instances folder" can be stored. Could use a command such as cobble config open or cobble config edit to open the config file in the default editor. May need a cobble config reload option to reload options for features like auto-backup.

Configuration options could also be set per-server.

List of options to add:

• New server world folder name Add option to create a server folder and automatically download server jar #1
• Backup interval Add backup subcommand #3
• Server instances folder Create a portable build #7