Change Skin -> Theme

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

Oqtane.Client/Themes/Controls/Login.razor

@@ -0,0 +1,41 @@
+@using Oqtane.Themes
+@using Oqtane.Shared
+@using Microsoft.JSInterop
+@inherits ThemeObjectBase
+@inject IUriHelper UriHelper
+@inject IJSRuntime jsRuntime
+
+<button type="button" class="btn btn-primary" onclick="@Click">@name</button>
+
+@functions {
+    string name = "";
+
+    protected override async Task OnInitAsync()
+    {
+        var interop = new Interop(jsRuntime);
+        string user = await interop.GetCookie("user");
+
+        if (user == "")
+        {
+            name = "Login";
+        }
+        else
+        {
+            name = "Logout";
+        }
+    }
+
+    private async Task Click()
+    {
+        if (name == "Login")
+        {
+            UriHelper.NavigateTo(PageState.Alias + "login");
+        }
+        else
+        {
+            var interop = new Interop(jsRuntime);
+            await interop.SetCookie("user", "", 7);
+            UriHelper.NavigateTo(PageState.Alias, true);
+        }
+    }
+}