(#100) - Use Blobs: normalize FileReader

Always use `reader.onloadend` and access data via `this.result`.
(#100) - Use Blobs (IndexedDB): Improvements

Improve `decode` option behaviour in `getAttachment`
and prevent base64 detour for inline attachments in Chrome.
(#100) - Use Blobs for attachments: WebSQL

Add Blob storage support for WebSQL.