Fix issue where urls with special characters were not correctly deserialized

[overcyn]

ORKPathRelativeToURL and ORKURLForRelativePath do not correctly mirror each other. ORKPathRelativeToURL percent encodes it's output whereas ORKURLForRelativePath does not percent decode it's input. These methods are used during serialization/deserialization, causing a restored ORKFileResult to not point at the same path as the original file result.

Fix is to replace the call to [NSURL fileURLWithFileSystemRepresentation:...] with [NSURL URLWithString:...]. This matches with the [standardizedURL absoluteString] call in ORKPathRelativeToURL. I do not believe it is necessary to check if the file is a directory given that we are not modifying the relative path. If the original url had a trailing slash, then the output path will have a trailing slash and vice versa.