ScaleManager documentation updates

- Clarified proper usage of `pageAlignVertically` and add note about 2.2
  change and how to obtain 2.1 behavior.

- Removed the `@readonly` status of the `parentIsWindow` and `parentNode`;
  these can be updated in a controlled manner.

- Added intra-hyperlinks

- Updated some ancillary documentation


Ref. https://github.com/photonstorm/phaser/issues/1422