Multiple select option in filechooser dialog

[jbroadway]

You should be able to select multiple images at once in certain cases, instead of reopening the dialog each time to select the next file.

[jbroadway]

Click should highlight files or images as selected and add them to a list, then when they click a 'Select' button it would return them all at once as an array.

Would introduce a new boolean multiple option to $.filebrowser which would be specified in both $.multi_file and $.multi_image to make those more intuitive to work with.