Update scratch-vm to the latest version 

chore(package): update scratch-render to version 0.1.0-prerelease.201…

Slider range change with decimal value support

Make the stage color picker work with touch.

A few modifications were made while making this test:
- Change the "defaultMin/Max" to just be called "min/max", and pass the state through to make the inputs a controlled component. It is best to make form elements controlled since it makes it more clear how data flows.
- Force the passed in data to always be of type `number`, and transform it in the constructor to always be of type `string`, and change the onOk to transform it back to a number. With inputs, it is best to be very explicit about data types, and make it clear where you are using strings and where you are using numbers.
- Do not reset the state to `0` when the field is blank, that makes typing into it very hard (only applies after making it a controlled field)
- Use consistent booleans. Since the VM uses `isDiscrete`, change it so we do not use any opposite flags (like `decimal`) for clarity.

Writing tests for this really helped me understand the behavior. If you read through the test descriptions and see anything you did not intend, let me know.

fix(UI): fix cursor property when hovering account nav items

fix(css): fix css value has mixed support warning

Update scratch-svg-renderer to the latest version 

Run pify package through babel loader.

chore(package): update scratch-vm to version 0.2.0-prerelease.2019030…

chore(package): update scratch-blocks to version 0.1.0-prerelease.155…

Closes #4626

chore(package): update scratch-vm to version 0.2.0-prerelease.20190304203619

Closes #4622

Add Boost extension "coming soon" tile

Update scratch link icon

Closes #4609

Closes #4558

Initial version of translated tutorial gifs

Step Ids and step file names did not follow a consistent pattern. To make it easier to automate in the future, things were renamed in the following ways:

StepId: camel case, prefix with the short name that we usually use to refer to the tutorial, e.g. name, music, chaseGame. Followed by a name for the step, e.g. nameAddSprite, nameAddBackdrop. When there are two of a step, add ‘2’ to the end e.g. nameAddSprite2

file-naming: all step files should be in the steps directory. The name is the ‘kebab’ case of the stepId, followed by the language-code, then the file extension. For example the english version of the file for `nameAddSprite` would be `name-add-sprite.en.gif`, `chaseGameAddSprite2` would be `chase-game-add-sprite2.en.gif`

chore(package): update scratch-vm to version 0.2.0-prerelease.2019022…

Update scratch-l10n to the latest version 

* thumbnails folder: thumbnail images for tutorials (multistep decks and videos). Images should not need translations (avoid text that would need translation in the image)
* steps folder: gif images associated with tutorial steps. Images can be translated. English (default) images have the extension `.en.gif`, other language images should replace the `.en` with the corresponding locale.
* renamed some of the steps files to be more consistent and a bit less redundant
* removed a couple of files that were no longer referenced
* revised webpack config to allow localized step files to be loaded from `/static` on www

Fixes #4253 by telling the vm the langauge when it is initialized.  B…