Introduced methods for decoding URI paths and path segments
Assets controller support for encoded paths, works on Windows

- Fixes #1593, which is a regression introduced by #1522 and c0a84ac.
- No longer uses File.toURI on the base directory, as this didn't
  work properly on Windows. Instead URL path decoding is done manually
  using `UriEncoding.decodePath`.
- Removed the test file "foo+bar: baz.txt" because it caused errors
  when unzipping the Play distribution on Windows. Our tests still
  adequately cover this case.