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/WebLogDataTests.fs

@@ -1,6 +1,6 @@
 /// <summary>
 /// Integration tests for <see cref="IWebLogData" /> implementations
-/// </summary> 
+/// </summary>
 module WebLogDataTests
 
 open System
@@ -25,14 +25,15 @@ let ``Add succeeds`` (data: IData) = task {
               Rss           =
                   { IsFeedEnabled     = true
                     FeedName          = "my-feed.xml"
-                    ItemsInFeed       = None 
+                    ItemsInFeed       = None
                     IsCategoryEnabled = false
                     IsTagEnabled      = false
                     Copyright         = Some "go for it"
                     CustomFeeds       = [] }
               AutoHtmx      = true
               Uploads       = Disk
-              RedirectRules = [ { From = "/here"; To = "/there"; IsRegex = false } ] }
+              RedirectRules = [ { From = "/here"; To = "/there"; IsRegex = false } ]
+              AutoOpenGraph = false }
     let! webLog = data.WebLog.FindById (WebLogId "new-weblog")
     Expect.isSome webLog "The web log should have been returned"
     let it = webLog.Value
@@ -48,6 +49,7 @@ let ``Add succeeds`` (data: IData) = task {
     Expect.isTrue it.AutoHtmx "Auto htmx flag is incorrect"
     Expect.equal it.Uploads Disk "Upload destination is incorrect"
     Expect.equal it.RedirectRules [ { From = "/here"; To = "/there"; IsRegex = false } ] "Redirect rules are incorrect"
+    Expect.isFalse it.AutoOpenGraph "Auto OpenGraph flag is incorrect"
     let rss = it.Rss
     Expect.isTrue rss.IsFeedEnabled "Is feed enabled flag is incorrect"
     Expect.equal rss.FeedName "my-feed.xml" "Feed name is incorrect"