Fixes #128 - non-collision and multiple users

In the interests of non-collision and multiple users, favorites files are now downloaded to a path that includes the user's b32username as well as the full path to the item (storage or share).

Previously:

`https://web-dc2.spideroak.com/storage/MGSXXZ6FMVVXY/DeviceName/Users/tommy/Pictures/best-pic-evar.png`

Would have been downloaded to:

`Download/SpiderOak/.favorites/DeviceName/Users/tommy/Pictures/best-pic-evar.png`

After this change, it would be downloaded to:

`Download/SpiderOak/.favorites/MGSXXZ6FMVVXY/storage/MGSXXZ6FMVVXY /DeviceName/Users/tommy/Pictures/best-pic-evar.png`