Rename it all to systems!

Merge branch 'master' into dev

Big refactor

Fix some interaction issues (#3857) ...

* Fix #3844

* Fix #3790

* Expand assertions in nested overlap tests.

Refactor: extract variables & fix doc (#3585) ...

* Refactor: extract variables & fix doc

* cosmetic

* Merge the changing of #3656

* Update SpriteRenderer.js

* Update SpriteRenderer.js

Support that cache Sprite as Bitmap directly. (#3855) ...

* Cache Sprite as Bitmap directly.

In the current pixi.js , when we want to cache a sprite as Bitmap, we have to put the sprite add to a container , like this : 
```
var texture = PIXI.Texture.from(img);
var container = new PIXI.Container();
var sprite = new PIXI.Sprite(texture);
sprite.cacheAsBitmap = true;
container.addChild(sprite);
var renderTexture = PIXI.RenderTexture.create(sprite.width, sprite.height);
renderer.render(container, renderTexture);
```

With this PR , use could cache the sprite directly : 
```
var texture = PIXI.Texture.from(img);
var sprite = new PIXI.Sprite(texture);
sprite.cacheAsBitmap = true;
var renderTexture = PIXI.RenderTexture.create(sprite.width, sprite.height);
renderer.render(sprite, renderTexture);
```

* Update cacheAsBitmap.js

resolve ambiguity raised in #3695 (#3843)

Should not apply padding when trimmed (#3858)

Texture / render textures working ...

Also created global uniformGroup
Broke up webGL to projection / renderTexture manager
I’m on to something here! Almost there..

Refactored from texture

More updates added the mini-runner

Move code into else , when it's useless (#3840) ...

* Move code in else , when it useless

* Update CanvasMeshRenderer.js

Dev texture update (#3820) ...

* use texture transforms

* Plane accounted for texture transform before, now we can remove it

* move TextureTransform to the core
"uploadUvTransform" setting

* some user shaders have no uTransform

* fix canvas

* better docs

* bucking lint

* lint. again.

* trailing spaces

* move TextureTransform back

Prepare plugin support for objects with multiple BaseTextures (#3830) ...

* Add ability for Prepare plugin to upload the all textures for AnimatedSprites

* Add a new function to loop through all the textures of an AnimatedSprite and add them to the queue
* Moved Duplicate `findBaseTextures` function from WebGL & Canvas Prepare to Base prepare as static
* Moved all the `findObjectType` methods to their appropiate class as static methods for consistency

* Updated Comments to reflect "static" not "private" methods

* Added the findTexturesForAnimatedSprites logic to the standard findBasicTextures

This cleans up the need to worry about ordering the registration of hooks and only calls upload once

* Split the prepare.register function into 2 registerFindHook & registerUploadHook

* Some simple cleanup before the PR

* comment formatting

* removed dependenvy on `extras` from prepare

* Fix small comment issues with pull request

Removed the [optional] reference in the comments for both
new register methods.
Added a small example to the docs

* Add deprecation method

* Added Check before calling hooks and reformatted JSDoc

Lint wouldn't pass without the params in the JSDoc

* added `instanceof` check and fixed up the return true only if a texture is found

TilingSprite matrix calculation fix (#3831)

Tweaked fromLoader

Sag / image / canvas all in! ...

Base texture replaced..

Don't call getter , use `texture.orig.*` directly. (#3785) ...

* Don't call  getter  again

Don't call  getter of `texture.width`/`texture.height` again.

* Update NineSlicePlane.js

Small Texture Cache enhancements (#3789) ...

* Textures track cache id and remove from cache in destroy.

* Added tests related to texture cache contents.

Merge branch 'master' into dev

Fix preparation of destroyed items (#3802) ...

* Added isDestroyed to DisplayObject, BaseTexture. Don't prepare destroyed items.

* isDestroyed -> _destroyed, marked as private

Merge branch 'master' into dev

@sivael's fix for cacheAsBitmap is leaking objects #3801

More texture / framebuffer stuffs

Texture rig and some renaming

Texture stuff working cubes + two deee

spritesheet url tests for #3715 (#3781)

Merge branch 'master' into dev

Fix another issue that was causing #3790 (#3800)

Pass one