Support Pixi v7 - Githubissues

Dependencies

Upgraded Cubism 4 framework from R4 to R7 (see changelog in CubismWebFramework)
Migrated to Pixi v7
Changed peer dependency to entire pixi.js instead of individual @pixi/* packages. This should prevent version conflicts which cause duplicate Pixi instances to be bundled (as in #109)

BREAKING: Moved model automation (update/hit-test/focus) into an Automator class. Now, to dynamically change these options, for example autoUpdate, use model.automator.autoUpdate = true instead of model.autoUpdate = true.
Added autoHitTest and autoFocus options to provide fine-grain controls of the old (deprecated) autoInteract option.
Added ticker option to allow passing a custom PIXI.Ticker instance.
Fixed an "unhandled Promise rejection" warning in the console when the texture fails to load. This does not change any actual logic.
Fixed a bug where the model's initial state depends on the time it's instantiated.
Removed unexpected package gh-pages from dependencies in package.json.