Added the Output class

The output class represents an operation's output data.

core/Output.h

+#ifndef EIIMAGE_OUTPUT_H
+#define EIIMAGE_OUTPUT_H
+
+#include <vector>
+#include <string>
+
+
+class QWidget;
+class Output {
+  public:
+    Output(std::string name) : _name(name) {}
+    virtual QWidget* getWidget() = 0;
+    virtual Output* clone() const = 0;
+  protected:
+    std::string _name;
+};
+
+#endif //!EIIMAGE_OUTPUT_H
\ No newline at end of file