Added chrome local storage (for browser extensions)

Vanilla localStorage doesn't share data across domains. To keep users logged across tabs / different websites, Chrome extensions need to access the login token anywhere by using the chrome.storage API (https://developer.chrome.com/apps/storage). It is asynchronous, hence the use of promises to get the localStorage data in this fork. Note: if used in a Chrome extension, you also have to ask your users the "storage" permission in the manifest.json file for it to work.