Added the class Plugin

A Plugin is a set of Operations intended to be encapsulated in a dynamic
link library.

core/Plugin.cpp

+#include "Plugin.h"
+
+Plugin::Plugin(std::string name) : _name(name) {
+}
+
+std::string Plugin::getName() {
+    return _name;
+}
+
+std::vector<Operation*> Plugin::getOperations() {
+    return _operations;
+}
+
+void Plugin::addOperation(Operation* operation) {
+    _operations.push_back(operation);
+}
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core/Plugin.h

+#ifndef EIIMAGE_PLUGIN_H
+#define EIIMAGE_PLUGIN_H
+
+#include <string>
+#include <vector>
+
+#include "Operation.h"
+
+class Plugin {
+  public:
+    Plugin(std::string name);
+    std::vector<Operation*> getOperations();
+    std::string getName();
+    
+  protected:
+    void addOperation(Operation*);
+    
+  private:
+    std::vector<Operation*> _operations;
+    std::string _name;
+};
+
+#endif //!EIIMAGE_PLUGIN_H
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