Migrate to .NET Core 3.0.

DiscImageChef.Server/appsettings.json

@@ -0,0 +1,13 @@
+{
+  "ConnectionStrings": {
+    "DefaultConnection": "server=localhost;port=3306;database=discimagechef;uid=dic;password=dicpass"
+  },
+  "Logging": {
+    "LogLevel": {
+      "Default": "Information",
+      "Microsoft": "Warning",
+      "Microsoft.Hosting.Lifetime": "Information"
+    }
+  },
+  "AllowedHosts": "*"
+}