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.
@lazd  I couldn't say about the quotes, but it is definitely not exclusively one form or the other.. double-quotes appear common for `defineProperty` usage, but single quotes are indeed used throughout as well.

The code uses `Object.defineProperty` exclusively to establish get/set properties. I'm not sure if it was initially chosen for particular reason or preference, but that would be too big a convention shift without a large consensus. When in Rome..