Disable dynamic, real-time toggling of the editor.

[mackron]

This is a cool feature, however it causes issues where the editor can tread on the toes of the main game as it's running because it shares some global state. The simplest and most robust way to resolve this is to just not allow the editor to be run at the same time as the game.

A command line switch "--editor" should be implemented which will cause the context to open the editor on start-up.