Warn before removing files

[jeffgca]

NB: Feature requests will only be considered if they solve a pain

Summary

We should make sure users want to remove a file, just in case they don't.

Problem

If I remove a file, I'd expect a confirmation prompt for a 1-way destructive action. I don't see any way in drive to recover files once removed, so I assume this is the case.

Impact

Users might accidentally remove a file by clicking on the wrong thing.

Solution

Get the user to confirm they actually want to remove the thing.