Add OG types to page/post, add rendering in page head (#52)

src/MyWebLog.Domain/ViewModels.fs

@@ -112,6 +112,9 @@ type DisplayPage = {
 
     /// <summary>The metadata for the page</summary>
     Metadata: MetaItem list
+
+    /// <summary>The OpenGraph properties for the page</summary>
+    OpenGraph: OpenGraphProperties option
 } with
 
     /// <summary>Create a minimal display page (no text or metadata) from a database page</summary>
@@ -128,7 +131,8 @@ type DisplayPage = {
           IsInPageList = page.IsInPageList
           IsDefault    = string page.Id = webLog.DefaultPage
           Text         = ""
-          Metadata     = [] }
+          Metadata     = []
+          OpenGraph    = None }
 
     /// <summary>Create a display page from a database page</summary>
     /// <param name="webLog">The web log to which the page belongs</param>
@@ -136,8 +140,9 @@ type DisplayPage = {
     /// <returns>A <c>DisplayPage</c> with text and metadata</returns>
     static member FromPage webLog page =
         { DisplayPage.FromPageMinimal webLog page with
-            Text     = addBaseToRelativeUrls webLog.ExtraPath page.Text
-            Metadata = page.Metadata
+            Text      = addBaseToRelativeUrls webLog.ExtraPath page.Text
+            Metadata  = page.Metadata
+            OpenGraph = page.OpenGraph
         }
 
 
@@ -1165,6 +1170,9 @@ type PostListItem = {
 
     /// <summary>Metadata for the post</summary>
     Metadata: MetaItem list
+
+    /// <summary>OpenGraph properties for the post</summary>
+    OpenGraph: OpenGraphProperties option
 } with
 
     /// <summary>Create a post list item from a post</summary>
@@ -1183,7 +1191,8 @@ type PostListItem = {
           CategoryIds = post.CategoryIds |> List.map string
           Tags        = post.Tags
           Episode     = post.Episode
-          Metadata    = post.Metadata }
+          Metadata    = post.Metadata
+          OpenGraph   = post.OpenGraph }
 
 
 /// <summary>View model for displaying posts</summary>