Input "enabled/disabled" API and documentation consistency updates

Updates wrt  https://github.com/photonstorm/phaser/issues/1191 - backwards compatible, no known issues.

The `disabled` property of various input classes has been inverted to `enabled` and direct/internal usage of `disabled` has been transformed to `!enabled`. This mirrors the positive-case usage found in almost all API: visible vs. hidden, exists vs notExists, etc.

A `disabled` get/set property has been added to wrap `enabled`, and marked as `@deprecated`. This ensures current API compatibility.
I use single quotes for everything other than `Object.defineProperty`, the only exceptions are classes contributed by third parties, like the Gamepad ones were (or I guess code written at 3am, but that should be far and few between). I change them if I spot them, but they're easy to miss. I could change them for defineProperty as well I guess, then they could be part of the jshint check, but it isn't like there aren't more important things to spend time on.

I decided not to use getters and setters in *property initializers* because it would lead to inconsistency for objects created from existing prototypes, which lots are. Which leaves either Object.defineProperty or Object.defineProperties. As the amount of actual code per get/set function is identical in each case, and as you'd still need the property label in `defineProperties`, all it would actually save is `});` from the end of each block. To me that makes it a change for the sake of change, rather than being of any actual benefit.