Netcore: Migration of more controllers (#8220)

* https://dev.azure.com/umbraco/D-Team%20Tracker/_workitems/edit/6587 - Migrated DictionaryController, TinyMceController and UpdateCheckController

* Removing connection string and changing to use the right variable

Co-authored-by: Elitsa Marinovska <elm@umbraco.dk>

src/Umbraco.Web.BackOffice/Controllers/ImageUrlGeneratorController.cs

@@ -9,7 +9,7 @@ using Umbraco.Web.Common.Attributes;
 using Umbraco.Web.Models;
 using Umbraco.Web.Mvc;
 
-namespace Umbraco.Web.Editors
+namespace Umbraco.Web.BackOffice.Controllers
 {
     /// <summary>
     /// The API controller used for getting URLs for images with parameters