needs "Exit Server" option and ability to connect to a different server in same session

[bonzaiferroni]

Currently the client needs to be closed and reopened to connect to another server. The main issue with connecting to a new server is that room and player info has been cached, and it needs to be reset. The easiest way to do this might be to break up the main scene into login and play. Upon connecting a new scene will load with new objects. To do this, the ScreepsAPI and associated classes need to DontDestroyOnLoad so they survive scene changes.