Add storage opt in hub. Can now configure localStorage or sessionStorage

[cyrilchapon]

Hello.

I made this because we needed support for sessionStorage option.

Changes :

• Hub() constructor now accepts a single opts arguments
  • opts.permissions behaves like previously permissions
  • opts.storage is added. Can be one of window.localStorage and window.sessionStorage (or any object with the same API, I guess). It defaults to window.localStorage

Compat checks with window.localStorage are now made to opts.storage

TODO : Some tests should be added to ensure

• Chosen storage is respected
• Unprovided storage defaults to localStorage
• Everything works like excepted