Generate brunch app using gh:brunch/dead-simple skeleton

[#73478504]

+ some customization in readme / package.json
Make sure that DrawingTool constructor is exported to the window object

[#73478504]

It requires a hacky approach, see:
https://github.com/brunch/brunch/issues/712

It's needed as we don't want to force users of our lib to call

  require('js/main');

before they can initialize DrawingTool.
Add simple example page that can be used during development

[#73478504]