Sound editor effects UI 

Add trimming to the sound editor

Update html-webpack-plugin to the latest version 

Add new icons for sprite and backdrop buttons

Change language selector colors so that options are visible in all browsers/OS.

Fix 404-ing costume in "Text" sprite

Changed color and background-color as requested; temporarily hidden the icon

Change default block zoom to 0.675 from 0.75

Use sound ID coming back from decodeSound

localeData cleanup

the background was white and the font color was too - I changed it to be black instead

Initial sound editor area with playback and renaming

move all locale data (react-intl/locale-data and gui messages) into locale.js. This also makes switching to an external node package easier because the package just needs to export the same thing as locale.js.