Refactor JS, remove Browserify, simplify JS for components

[krijnhoetmer]

• Only 1 JS file per component, aligning with CSS (includes handlers and/or decorators).
• Less duplicate code (less var dom = require( 'helpers/dom' ); lines; using the ohnl global now (opinionated, I know)).
• Component JS are included automatically (handlers.js and decorators.js no longer required, no need to manually list all included components - less Naming Things).
• Handlers/Decorators need to be registered from within each component; duplicates are now logged.
• All JS is now included in one file (main.js); polyfills is concatenated as well.