Load configuration from a yaml file

[MarshallAsch]

Is your feature request related to a problem? Please describe.

Having to pass all the configuration through as cli flags or envirionment variables can be frustrating if the same configuration is used for a number of different course configurations.

Describe the solution you'd like

This should load the configuration parameters from configuration files.

A hierarchy (higher takes priority):

1. ~/.scioer.yml
2. ~/.config/scioer/config.yml
3. $XDG_CONFIG_HOME/scioer/config.yml
4. /etc/scioer/config.yml

A specific configuration file can be specified with the --config <file> or ignored with the --no-config options.

Describe alternatives you've considered

This should tie into the configuration order of precedence with #43, #44, and #45.