Implement a basic FormData support, used to serialize the POST body.

Use xhr2 library to replicate XHMLHttpRequest.

Desactivate all broken storages (IndexedDB, localstorage, webdav, ...) which rely on browser API.

Thanks to Aurelien Calonne <aurel@nexedi.com> and Guillaume Royer <guillaume.royer@clearroad.io> for their contributions.