Photo Gallery Feature Updates

[timbuckingham]

Add the ability to upload multiple photos at once to a photo gallery.
Not sure what the best way to approach this is, whether drag and drop or just allow multiples in the file dialog.

It would also be nice if we could allow more than just a caption, but maybe that should be left to the Matrix field type.

[timbuckingham]

Most of this made its way into the Media Gallery field type. We'll keep the fancy stuff there for 4.3, maybe integrate into core in 4.4.