modified ITheme interface (#344)

* upgrade to .NET Core 3.2 Preview 3 and fixes for issues created by #314

* Components based on Bootstrap4 for Sections and  TabStrip to increase productivity and promote uniformity in Module UIs

* rolled back change creating an Infrastructure.Interfaces namespace, modified IModule interface to be strongly typed

* modified ITheme interface

Oqtane.Client/Themes/ITheme.cs

@@ -1,10 +1,9 @@
-using System;
-using System.Collections.Generic;
+using Oqtane.Models;
 
 namespace Oqtane.Themes
 {
     public interface ITheme
     {
-        Dictionary<string, string> Properties { get; }
+        Theme Theme { get; }
     }
 }