This use of shouldComponentUpdate is wrapping the incorrect use of bind
in the mapStateToProps call.

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.

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.

- Call scrollToCategoryByName('My Blocks') after custom block is created
- Cannot assume custom blocks section will be last category
- May pose issue during localization efforts

Use the same drag threshold as from the blocks. It may need to be dialed
in further, but testing will be needed.

Showing/hiding 'more options' in the different types of variable prompts based on var type provided from scratch blocks

This, along with the related VM pull request, fixes LLK/scratch-vm#865.
This adds the GUI code which posts wheel scroll data to the VM's
mouseWheel IO (which, in turn, activates relevant "when key pressed"
blocks).

Remove the WebGL checks from the error boundary. Instead, just do not
render the stage if it is not supported.

* Added object.assign polyfill

* Fix IE load failure

Don’t call `(window.AudioContext || window.webkitAudioContext)()` if platform is IE

Catch any other errors, and display Browser unsupported in error-boundary.

If for some reason there are no other errors (unlikely), preview-modal will still check for IE and show the unsupported modal.

Polyfilling Object.assign is enough to get through load and show the modal for IE. We can always switch to `babel-polyfill` if there are others needed later, but for now this is smaller.