Migrated MidiTest to unified API
Migrated MonoCatalog-MonoDevelop to unified api

- Added "using System;" in order to use nfloat
- Cast nfloat to float
- Cast nint to int so that cast to enum would work
- Cast NSString to string
- Changed RectangleF.Emoty to CGRect.Empty
- Changed SizeF.Empty to CGSize.Empty
- Changed System.Drawing.CGRect to CGRect
- PointF.Empty to CGPoint.Empty