UIProgressView default property added - fixes #571
Duplicate default entries removed
Virtual Convert and ConvertBack methods in MvxNativeValueConverter
Merge pull request #572 from damirarh/VirtualMvxNativeValueConverter

Virtual Convert and ConvertBack methods in MvxNativeValueConverter
Merge branch 'v3.1' of github.com:slodge/MvvmCross into v3.1