A hotfix for sprites batching drawOrder (playcanvas#1594)

Library code assets (playcanvas#1566)

* Set asset to loaded if it's a library script

Text-element render sub-range (playcanvas#1585)

* added text-element sub-range
* using two separate properties for range start and end
* expose range start and end in ElementComponent
* small doc update

Revent hierarchy sync optimization.

AssetListLoader (playcanvas#1582)

Fix syntax error

Add missing button sprite assets used in the example code (playcanvas…

…#1575)

Revert negative scale fix.

Flip face culling if camera_flip or world_mat only (playcanvas#1569)

Retry http requests when loading resources (playcanvas#1553)

* [ADD] Add retry, maxRetries, maxRetryDelay options to http request methods
* Document new http options
* [ADD] pc.ResourceLoader#enableRetry and pc.ResourceLoader#disableRetry