Change Skin -> Theme

To better align with commonly used terminology in industry renamed all references from Skin -> Theme.

Oqtane.Server/Controllers/ThemeController.cs

@@ -0,0 +1,25 @@
+using System.Collections.Generic;
+using Microsoft.AspNetCore.Mvc;
+using Oqtane.Repository;
+using Oqtane.Models;
+
+namespace Oqtane.Controllers
+{
+    [Route("{site}/api/[controller]")]
+    public class ThemeController : Controller
+    {
+        private readonly IThemeRepository themes;
+
+        public ThemeController(IThemeRepository Themes)
+        {
+            themes = Themes;
+        }
+
+        // GET: api/<controller>
+        [HttpGet]
+        public IEnumerable<Theme> Get()
+        {
+            return themes.GetThemes();
+        }
+    }
+}