Change the JSON seriasiable data classes to use an explicit static
fromJSON method and an optional toJSON method for turning them to and
from JSON.
This improves over the previous pattern of passing the JSON to the
constructor as it frees up the constructor to be able to take whichever
argument types suits the code instead of being beholden to the JSON
serialised form.
The role of a slave as a host for Factorio servers is not well reflected
in its name and has caused confusion among users. Rename slave to host
to better reflect its role as a host of Factorio servers.
The role of the master server as the party controlling every part of the
cluster is not well reflected in its name and has caused confusion among
users on several occasions. Rename master to controller to better
reflects its role.