Create and show a mask covering the inspector when the user drags a zip file over the browser
Merge pull request #125 from hatched/inspector-zip-droptarget

__To QA__
- open app.js and place a breakpoint on line 686 & 730
- deploy a service and open its inspector
- drag a .zip from your desktop over the browser, it should hit your first breakpoint
- remove the first breakpoint and click continue
- drag a .zip from your desktop and drop on the open inspector, it should trigger the second breakpoint
- done!

__Note__
Until we get designs from UX about this mask it's transparent so it isn't discoverable.