Episode update v.20

This is a small update to the Episode which:

• Adds a loading screen (to fix the stuttering caused by the initial asset preload). Pro tip: you can still press ESC to skip the loading screen (although of course the loading will still continue in the background, potentially causing stutters for a few seconds).

• Adds the "automatic" option for letterboxing (which will stretch up to 20%, then letterbox beyond that).

Due to changes to some internal files, this update will regrettably reset any in-progress mission, and also any Options relating to Graphics/Sound/Controls/etc.