[ADD] Authentication view for connecting SideStore to an Apple ID

AltStore/View Extensions/Styles/FilledButtonStyle.swift

@@ -0,0 +1,47 @@
+//
+//  FilledButtonStyle.swift
+//  SideStore
+//
+//  Created by Fabian Thies on 29.11.22.
+//  Copyright © 2022 SideStore. All rights reserved.
+//
+
+import SwiftUI
+
+struct FilledButtonStyle: ButtonStyle {
+    var isLoading: Bool = false
+    
+    func makeBody(configuration: Configuration) -> some View {
+        ZStack {
+            configuration.label
+                .opacity(isLoading ? 0 : 1)
+            
+            if isLoading {
+                ProgressView()
+                    .progressViewStyle(CircularProgressViewStyle())
+            }
+        }
+        .foregroundColor(.white)
+        .multilineTextAlignment(.center)
+        .frame(maxWidth: .infinity)
+        .padding()
+        .background(
+            RoundedRectangle(cornerRadius: 12)
+                .foregroundColor(.accentColor)
+        )
+        .opacity(configuration.isPressed || isLoading ? 0.7 : 1)
+        .disabled(isLoading)
+    }
+}
+
+struct FilledButtonStyle_Previews: PreviewProvider {
+    static var previews: some View {
+        SwiftUI.Button {
+            
+        } label: {
+            Label("Test Button", systemImage: "testtube.2")
+                .buttonStyle(FilledButtonStyle())
+        }
+
+    }
+}