(#100) - Use Blobs for attachments: Tests

Add tests for Blob usage.
(#100) - Detect IndexedDB Blob support
(#100) - Use Blobs for attachments: IndexedDB

Add Blob storage support for IndexedDB.
(#100) - Use Blobs for attachments: HTTP

Add Blob storage support for HTTP adapter.
(#100) - Fix empty attachment blobs: HTTP

Chrome reads `new Blob([null])` as "null", whereas FF reads it as "".
(#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.