Blob mimetype not saved consistently across drivers

[thgreasi]

As discussed on #322, WebSql and localStorage drivers lose the mimetype of Blobs. It works just on IndexedDB.

Keep in mind that PhantomJS < 2.0 does not support the Blob constructor.

[stakach]

Loading videos from blobs hits this issue on Safari - also it looks like the latest safari is still having the blobs serialized, however it supports IndexDB according to caniuse

[tofumatt]

Unfortunately the iOS8/Yosemite versions of Safari DO support IndexedDB but have issues that means we can’t yet use them in localForage. (#254)