Remove & redirect outdated articles

[petele]

Removes & redirects outdated articles including:

• https://www.html5rocks.com/en/tutorials/es6/promises/
• https://www.html5rocks.com/en/tutorials/offline/quota-research/
• https://www.html5rocks.com/en/tutorials/webdatabase/websql-indexeddb/
• https://www.html5rocks.com/en/tutorials/offline/takingappoffline/
• https://www.html5rocks.com/en/tutorials/offline/whats-offline/
• https://www.html5rocks.com/en/tutorials/offline/storage/

Updates deprecation notice on HTML Imports