Multiple file upload for costumes, sounds, backdrops and sprites

Merge pull request #4512 from LLK/revert-4501-greenkeeper/scratch-render-0.1.0-prerelease.20190206213754

Revert "Update scratch-render to the latest version "

chore(package): update scratch-vm to version 0.2.0-prerelease.2019020…

Closes #4506

Use blob download instead of data-uri to enable large downloads

This was already being used for sb3s and sprite3s, but the code was repeated in different places. Make a single helper that downloads blobs, and make all download paths use it.

chore(package): update scratch-vm to version 0.2.0-prerelease.2019020…

Closes #4503

Update scratch-render to the latest version 

Update scratch-blocks to the latest version 

Update scratch-l10n to the latest version 

Update scratch-blocks to the latest version 

chore(package): update scratch-vm to version 0.2.0-prerelease.2019020…

Closes #4480

Wait until loader becomes stale to continue in project loader tests

Escape special characters in toolbox xml

Including sprites, backdrops, costumes and sounds inputs

Fix "See Inside" not showing variables

Fix issue #4431 by change 'dserver' to 'server'

I needed to update the player css because the editor side wasn't large enough to be useable.

We can't rely on refreshWorkspace always causing a toolbox update, so make sure to update the toolbox manually if it is needed.

Call updateToolbox after adding new blocks from the backpack.