I also suspect this will fix some of the times when the menu
mysteriously stayed open, because it was being re-rendered for by
mistake.

Add new asset menu system

This makes it possible to use on iOS/touch

Duplicate costume

Add duplicate button. Pass the costume ID to paint (the previous costume ID used matches when duplicate is used.) When switching to the costume tab, open the current costume.

Fix deleting in sprite selector item event bubbling

This is required because you can delete the last sound, and without a re
render the tab will continue to render the sound editor, causing an
error.

Update gui to use getter for target costumes

Move active tab state into a reducer

Greenkeeper updates 2 22 18

Closes #1450

Closes #1461

Closes #1445

Remove enableExtensions prop

Fixed issue #1409

Update scratch-paint to the latest version 

Fix issue 1212

Detect wheel event on canvas and post data to VM