Improve Image Uploader

[wlaurance]

We want to support adding multiple files at once.

We want to see a preview of images.

We want to be able to reorder the images.

[petergault]

1. Upload a group of images (perhaps drag and drop?)

2. Show a thumbnail of the images.

3. Allow teachers to order the images either through drag and drop or by setting the number from a drop down. If an item is set at 11, and I reset it to 1, it should bump 1 to 2, 2 to 3, 3 to 4, etc. Always +1 to the subsequent after the reset number.

[petergault]

Possible tool to use:
https://github.com/danialfarid/angular-file-upload