Move OpenGraph property generation to models (#52)

- Add auto-OpenGraph field to web log
- Only generate properties for posts/pages without them if this flag is set
- Set flag to yes on v3 database migration
- Add JSON converter for OpenGraph type
- Add tests for models

src/MyWebLog.Tests/Data/PostDataTests.fs

@@ -1,6 +1,6 @@
 /// <summary>
 /// Integration tests for <see cref="IPostData" /> implementations
-/// </summary> 
+/// </summary>
 module PostDataTests
 
 open System
@@ -54,7 +54,7 @@ let ``Add succeeds`` (data: IData) = task {
         { Id              = PostId "a-new-post"
           WebLogId        = WebLogId "test"
           AuthorId        = WebLogUserId "test-author"
-          Status          = Published 
+          Status          = Published
           Title           = "A New Test Post"
           Permalink       = Permalink "2020/test-post.html"
           PublishedOn     = Some (Noda.epoch + Duration.FromMinutes 1L)
@@ -66,7 +66,8 @@ let ``Add succeeds`` (data: IData) = task {
           Episode         = Some { Episode.Empty with Media = "test-ep.mp3" }
           Metadata        = [ { Name = "Meta"; Value = "Data" } ]
           PriorPermalinks = [ Permalink "2020/test-post-a.html" ]
-          Revisions       = [ { AsOf = Noda.epoch + Duration.FromMinutes 1L; Text = Html "<p>Test text here" } ] }
+          Revisions       = [ { AsOf = Noda.epoch + Duration.FromMinutes 1L; Text = Html "<p>Test text here" } ]
+          OpenGraph       = Some { OpenGraphProperties.Empty with Type = VideoMovie } }
     do! data.Post.Add post
     let! stored = data.Post.FindFullById post.Id post.WebLogId
     Expect.isSome stored "The added post should have been retrieved"
@@ -87,6 +88,7 @@ let ``Add succeeds`` (data: IData) = task {
     Expect.equal it.Metadata post.Metadata "Metadata items not saved properly"
     Expect.equal it.PriorPermalinks post.PriorPermalinks "Prior permalinks not saved properly"
     Expect.equal it.Revisions post.Revisions "Revisions not saved properly"
+    Expect.equal it.OpenGraph post.OpenGraph "OpenGraph properties not saved correctly"
 }
 
 let ``CountByStatus succeeds`` (data: IData) = task {