Fix BL-734 & BL-712, allow windows UNC paths

There may be more path-related issues that will turn up with testing,
but this gets us past the obvious creation/editing/saving of a book
on //localhost, so that testing can commence.
Merge pull request #135 from BloomBooks/BL-734+BL-712

Fix BL-734 & BL-712, allow windows UNC paths