LPS-33667 First changes to validate LAR files before updating

Hey Nate, 

I only need you to review the first 3 commits (js) and the last one (css). The rest can go directly to Brian.

I am using the drag-and-drop uploader for 1 single file (LAR file) to reuse all the infrastructure of the temporary files since we need to store the LAR files temporarily to do an exhaustive validation.

Thank you!