add DSynchronize like feature - delete and add folders

```
Long time user of cryptsync here.

One issue I have is that empty folders are not added or deleted.

But this is possible, this program here does it just fine...

http://dimio.altervista.org/eng/

Only it doesnt encrypt the files.

```

Original issue reported on code.google.com by `bl...@blakeking.com` on 20 Feb 2015 at 12:00
