Extend basic workspace operations +,-,*,/ to allow hetergenous workspaces

[NickDraper]

This involves extending the iterator class to loop over the smaller workspace repeatedly. You will need to consider and implement sensible rules to control if the operation is valid.

Also consider adding workspace operator overloads as unowned methods in the API namespace that will allow workspaces to be added using code such as
W1= W2 + W3;

eg. (note this is not correct but gives an idea)

```
#include “MantidKernel/System.h”
#include “MantidAPI/IAlgorithm.h”
#include “MantidAPI/Workspace.h”
#include “MantidKernel/Logger.h”

#include “boost/shared_ptr.hpp”
namespace Mantid
{
namespace API
{
// Workspace operator overloads
typedef boost::shared_ptr`` wsp_ptr;

wsp_ptr DLLExport operator+(const Workspace& lhs,const Workspace& rhs); wsp_ptr DLLExport operator-(const Workspace& lhs,const Workspace& rhs); wsp_ptr DLLExport operator*(const Workspace& lhs,const Workspace& rhs); wsp_ptr DLLExport operator/(const Workspace& lhs,const Workspace& rhs); }

}
```

The operator overloads would

- Using the algorithmManager to get the correct algorithm as a child algorithm
- Set the input workspaces of the algorithm and execute it
- Extract and return the output workspace.

[NickDraper]

This issue was originally trac ticket 75