Apply better screen nomenclature to video system

[MooglyGuy]

Currently the code uses a bunch of different terms, sometimes interchangeably, for what ends up being four different conceptual things:

Screen: The video output from a driver. A driver can output 0..N screens.
Display: The physical device displaying 1..N screens. In real life, this can be a raster CRT, many different kinds of LCD, a vector CRT, or even multiple superimposed video outputs on one raster CRT.
Window: The display area on the host machine. A host machine can have 1..N windows.
View: The manner in which 0..N displays are shown on a given window.

For example, in a Cocktail View of a 1-Screen game, there will be 2 Displays shown in 1 Window, with each Display showing the output of that single Screen, but with different transforms.

These associations are simple and easy to remember, but due to different people working on different parts of the overall "video signal chain" code in MAME, over wildly different time periods, much of the code has not been structured with this in mind. So, someone (probably me) needs to go through and make the code more robust, and rename things for clarity as needed.

[ghost]

Also noting here (way late, but still important) that documentation will need to follow the nomenclature of the code when that gets settled.