Moved files and introduced IMarkdownToHtmlConverter to avoid packages to handle markdown in core

Signed-off-by: Bjarke Berg <mail@bergmania.dk>

src/Umbraco.Core/HealthCheck/NotificationMethods/IHealthCheckNotificationMethod.cs

@@ -0,0 +1,14 @@
+using System.Threading;
+using System.Threading.Tasks;
+using Umbraco.Core.Composing;
+using Umbraco.Infrastructure.HealthCheck;
+
+namespace Umbraco.Web.HealthCheck.NotificationMethods
+{
+    public interface IHealthCheckNotificationMethod : IDiscoverable
+    {
+        bool Enabled { get; }
+
+        Task SendAsync(HealthCheckResults results);
+    }
+}