Code cleanup to facilitate transfer to PCL

Bar.cs :
* Change type of color property to int, to prevent dependency on
System.Drawing
* Make class Bar implement IDataObject, to enable DataArray implementing
IEnumerable<IDataObject>
* Make ProviderId property public to comply with IDataObject interface

BarSeries.cs :
* Change fList type to List<IDataObject> (non-generic ArrayList class
not available in PCL)
* Make DataArray implement IEnumerable<IDataObject> instead of
non-generic IEnumerable (requires implementation of generic
GetEnumerator() method and explicit implementation of non-generic
GetEnumerator() )

FormUtility.cs :
* Remove redundant "using System.Web"