[Ide] Bug21992 - Open File dialog error when selecting text encoding

Problem was that some code used "MonoDevelop.Ide.SelectEncodingsDialog.ConversionEncodings" and some "MonoDevelop.Projects.Text.ConversionEncodings" property... So I removed "MonoDevelop.Ide.SelectEncodingsDialog.ConversionEncodings".

Since SelectedEncodings.ConversionEncodings  was int[] and TextEncoding.ConversionEncodings is TextEncoding I had to do some conversions...