Add File Dialog Features related to selection

[makermelissa]

The file dialog is working great and pretty much as intended, but a couple of other features would really make it shine.

Multiple File Selection
It would be nice to be able to hold down Shift and/or Command/Ctrl to select multiple files (I like how it works better in Windows than Mac personally). Then the following operations could be done:
Delete, Download, Move

Deselect
This would probably go hand-in-hand with multiple file selection and would yield the same results as when a folder is first entered.

Refresh
This would simple retrieve the list of files again. It would probably be easiest to deselect the files, but perhaps a list could be compared and if the currently selected files still exist, maintain the selection.

[makermelissa]

Currently working on this and I have the selection mechanism working prefectly, but many of the file operations need to be adjusted to handle multiple files better such as deleting and downloading.