Adds interfaces for IContent, IMedia, IContentBase.

Adds interfaces for IContentTypeBase, IContentTypeComposition, IContentType and IMediaType.
This includes the inheritance structure for Content and Media, as well as ContentType and MediaType which is basically the same except for Templates and Compositions.

src/Umbraco.Core/Models/IContent.cs

@@ -0,0 +1,56 @@
+using System;
+
+namespace Umbraco.Core.Models
+{
+    /// <summary>
+    /// Defines a Content object
+    /// </summary>
+    public interface IContent : IContentBase
+    {
+        /// <summary>
+        /// Alias of the template used by the Content
+        /// This is used to override the default one from the ContentType
+        /// </summary>
+        string Template { get; set; }
+
+        /// <summary>
+        /// Boolean indicating whether the Content is Published or not
+        /// </summary>
+        bool Published { get; }
+
+        /// <summary>
+        /// Language of the data contained within the Content object
+        /// </summary>
+        string Language { get; set; }
+
+        /// <summary>
+        /// Gets the Guid Id of the Content's Version
+        /// </summary>
+        Guid Version { get; }
+
+        /// <summary>
+        /// Gets or Sets the date the Content should be released and thus be published
+        /// </summary>
+        DateTime? ReleaseDate { get; set; }
+
+        /// <summary>
+        /// Gets or Sets the date the Content should expire and thus be unpublished
+        /// </summary>
+        DateTime? ExpireDate { get; set; }
+
+        /// <summary>
+        /// Changes the <see cref="IContentType"/> for the current content object
+        /// </summary>
+        /// <param name="contentType">New ContentType for this content</param>
+        /// <remarks>Leaves PropertyTypes intact after change</remarks>
+        void ChangeContentType(IContentType contentType);
+
+        /// <summary>
+        /// Changes the <see cref="IContentType"/> for the current content object and removes PropertyTypes,
+        /// which are not part of the new ContentType.
+        /// </summary>
+        /// <param name="contentType">New ContentType for this content</param>
+        /// <param name="clearProperties">Boolean indicating whether to clear PropertyTypes upon change</param>
+        void ChangeContentType(IContentType contentType, bool clearProperties);
+    }
+}