Add support for automatic client side resizing of images, pre-upload.

[MattWilcox]

This is possibly a way for enhancing image upload fields in the CMS, and while not complete this seems to be a good chunk of that work already done:

https://pqina.nl/blog/compress-image-before-upload/

We (too often) hit an issue where clients will try to upload print-size media that is vastly too large in terms of pixel dimensions (not filesize). This can break things because the memory allocation of doing anything with a canvas so large just kills GD/Imagik/PHP.

We already use a plugin "Image Resizer" to automatically reduce images over 2200px x 2200px after upload, so that excessive images are not stored in the asset buckets... but we also often hit issues where the source image uploaded is so massive that even Image Resizer chokes.

This looks like a great possibility to have that browser transparently pre-scale enormous images before the upload even happens.

Would love to see Craft support this sort of thing.