Made the re/undo code from the branch work in this, this is a manual copy as something went horribly wrong with the repository. Before building I first want to check if everything is there.[skip ci]

GreenshotPlugin/Interfaces/Drawing/IFieldholder.cs

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+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2015 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: http://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using System.Collections.Generic;
+
+namespace GreenshotPlugin.Interfaces.Drawing
+{
+	/// <summary>
+	/// Any element holding Fields must provide access to it.
+	/// AbstractFieldHolder is the basic implementation.
+	/// If you need the fieldHolder to have child fieldHolders,
+	/// you should consider using IFieldHolderWithChildren.
+	/// </summary>
+	public interface IFieldHolder
+	{
+
+		event FieldChangedEventHandler FieldChanged;
+
+		void AddField(IField field);
+		void RemoveField(IField field);
+		IList<IField> GetFields();
+		IField GetField(IFieldType fieldType);
+		bool HasField(IFieldType fieldType);
+		void SetFieldValue(IFieldType fieldType, object value);
+	}
+
+	/// <summary>
+	/// Extended fieldHolder which has fieldHolder children.
+	/// Implementations should pass field values to and from 
+	/// their children.
+	/// AbstractFieldHolderWithChildren is the basic implementation.
+	/// </summary>
+	public interface IFieldHolderWithChildren : IFieldHolder
+	{
+		void AddChild(IFieldHolder fieldHolder);
+		void RemoveChild(IFieldHolder fieldHolder);
+	}
+}