Trigger events when moving, creating or deleting files/directories

[Alhadis]

Redux of #938, which I closed after deciding it was a menial addition that was just bloating your already creaking PR backlog.

Turns out there's a pretty severe concurrency issue involved here. I tried making-do with file-system events and path-watching, and I've found it's actually impossible to monitor the order of events when dragging and dropping.

Example:

1. A package listens for every new file that's been created or changed, and updates the paths accordingly.
2. A user moves a file through the tree-view's rename
3. The tree-view requests an icon for a file path that the package doesn't know is an existing file that's already been matched
4. Package registers the "new" path as an entirely separate file
5. Package has no way of knowing whether that was a copy or a move

So... yeah, since this is actually a pretty visible and very tangible problem, I'm reopening.