Fix handleExtensionAdded when no targets present

Manually fire tab change events onclick to fix touching tabs not working

Merge pull request #1733 from LLK/greenkeeper/scratch-vm-0.1.0-prerelease.1523023502-prerelease.1523023526

Update scratch-vm to the latest version 

It seems like there is some kind of touch action interference coming
from the blocks panel, where if you touch the tabs on a touchscreen
chromebook/chrome responsive mode, it does not select the tab if the
touch radius is overlapping the blocks panel at all. See gifs in PR for
more explanation. Fixes issue #1283, making chromebooks useable!

Merge pull request #1729 from LLK/greenkeeper/scratch-vm-0.1.0-prerelease.1522969014-prerelease.1522969034

Update scratch-vm to the latest version 

chore(package): update scratch-paint to version 0.2.0-prerelease.2018…

Merge pull request #1723 from LLK/greenkeeper/scratch-vm-0.1.0-prerelease.1522944347-prerelease.1522944370

chore(package): update scratch-vm to version 0.1.0-prerelease.1522944…

If an extension is loaded at project-load time, there won't be any
targets. In that case, `handleExtensionAdded` now skips target-specific
steps.

This change also adds a filter for JSON block info to support upcoming
block separators, which have XML but no JSON.

Closes #1721

Store sample rate/count for recorded sounds

Closes #1720

Make the stage thumbnail match the comps

Update design for editor tabs with icons, changing blocks to code.

Update scratch-paint to the latest version 

Language Selector Tool Tip Fix 

Resolves https://github.com/LLK/scratch-gui/issues/1713

update fork

Enable video sensing extension

merge updates to my fork

Show the costume/sound number similar to Scratch 2.

Update scratch-paint to the latest version 

Update scratch-paint to the latest version 

Add a jest unit test for making sure the number is rendered out when
provided and not when not provided.

Update scratch-paint to the latest version 

Merge pull request #1696 from LLK/greenkeeper/scratch-vm-0.1.0-prerelease.1522355889-prerelease.1522355906

Update scratch-vm to the latest version