Add class name props to the components, and fix positioning for the green flag to be reusable.

Still missing is a green flag, but blocks run!

This way one can still get the benefits of the GUI container but have a custom collection of components within it.

This shouldn't be required.

This way a stage is not necessary for sound blocks to work

Sprite info area design updates

Update eslint packages and fix indentations

Fix all lint warnings except todo comments (including a bug!)

Context menu

Update webpack and related packages

Confine add buttons to stage and sprite selectors

Update react-modal to the latest version 

Update wav-encoder to the latest version