Misleading error message when a column is not found

- version 1.5.0-preview

When I tried to create a prediction engine for one of my first models, I received an `ArgumentOutOfRangeException`. I think the error message means to tell me that the column named 'Features1' with the role 'Feature' was not found.
I would have expected to see my input, 'Features1', in quotes, rather than the column role, which should only take fixed values anyway.

_Feature column 'Features1' not found_ would have come more naturally to me.

https://github.com/dotnet/machinelearning/blob/78c406cf1f4a72751e389074e2f88574fafee8ea/src/Microsoft.ML.Core/Data/RoleMappedSchema.cs#L229

```Csharp
An exception of type 'System.ArgumentOutOfRangeException' occurred in Microsoft.ML.Core.dll but was not handled in user code: 'Features1 column 'Feature' not found'
at Microsoft.ML.Data.RoleMappedSchema.MapFromNames(DataViewSchema schema, IEnumerable`1 roles, Boolean opt)
at Microsoft.ML.Data.RoleMappedSchema..ctor(DataViewSchema schema, IEnumerable`1 roles, Boolean opt)
at Microsoft.ML.Data.GenericScorer.Bindings.Create(IHostEnvironment env, ISchemaBindableMapper bindable, DataViewSchema input, IEnumerable`1 roles, String suffix, Boolean user)
at Microsoft.ML.Data.GenericScorer.Bindings.ApplyToSchema(IHostEnvironment env, DataViewSchema input)
at Microsoft.ML.Data.GenericScorer..ctor(IHostEnvironment env, GenericScorer transform, IDataView data)
at Microsoft.ML.Data.GenericScorer.ApplyToDataCore(IHostEnvironment env, IDataView newSource)
at Microsoft.ML.Data.RowToRowScorerBase.ApplyToData(IHostEnvironment env, IDataView newSource)
at Microsoft.ML.Data.PredictionTransformerBase`1.Microsoft.ML.ITransformer.GetRowToRowMapper(DataViewSchema inputSchema)
at Microsoft.ML.PredictionEngineBase`2..ctor(IHostEnvironment env, ITransformer transformer, Boolean ignoreMissingColumns, SchemaDefinition inputSchemaDefinition, SchemaDefinition outputSchemaDefinition)
at Microsoft.ML.PredictionEngine`2..ctor(IHostEnvironment env, ITransformer transformer, Boolean ignoreMissingColumns, SchemaDefinition inputSchemaDefinition, SchemaDefinition outputSchemaDefinition)
at Microsoft.ML.PredictionEngineExtensions.CreatePredictionEngine[TSrc,TDst](ITransformer transformer, IHostEnvironment env, Boolean ignoreMissingColumns, SchemaDefinition inputSchemaDefinition, SchemaDefinition outputSchemaDefinition)
at Microsoft.ML.ModelOperationsCatalog.CreatePredictionEngine[TSrc,TDst](ITransformer transformer, Boolean ignoreMissingColumns, SchemaDefinition inputSchemaDefinition, SchemaDefinition outputSchemaDefinition)
```