Add web_root option to the master server and use it create URLs for
resources hosted by it. This permits hosting the master server web
interface behind reverse proxy under a dedicated path.
Allow the factorio_directory specified in the slave config to contain
multiple Factorio installs and add factior.version instance option to
select which install to use for the given instance.
Replace current configuration mess with a trimmed down version of the
original vision of #200. Configs are collection of config groups that
have fields that can be set. These groups allow organizing the fields
as well as opertunity for plugins to add their own groups. By default
plugins have an auto generated group with the enabled field.
Hornwitser