Add two new cross-platform methods to PathUtilities

- PathUtilities.OpenDirectoryInExplorer opens the directory in
  Explorer or the default file manager.
- PathUtilities.OpenFileInApplication opens a file in the default
  application (like double clicking on the file in explorer).

Change-Id: I199897ca5fe2c3fb78b13a7f71a5e21c7ca36457
Fix bug on Windows side of SelectFileInExplorer

Windows wants a comma after the /select parameter in order to really
select the file.

Change-Id: I5206be221316da1e399dbe92a38a630ab826a83f
Merge pull request #106 from ermshiperete/MorePathUtilties

Add two new cross-platform methods to PathUtilities