DeleteFile should not throw FileNotFoundException

It doesn't throw on Android or iOS (File.Delete default behavior).
Use the tel uri in windows store for phone calls

This is handled by Skype but not Skype specific (RFC3966).
Merge pull request #678 from guillaume-fr/patch-2

Use the tel uri in windows store for phone calls
Merge pull request #671 from guillaume-fr/patch-1

DeleteFile should not throw FileNotFoundException