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 

Sound editor  effects backend

Add end-to-end testing using selenium-webdriver

Update react-modal to the latest version 

Add undo/redo functionality and tests to sound editor

Allow GUI to fit into 1024px screen widths

Update wav-encoder to the latest version