Add redesigned custom dialog (#90)

lib/widgets/dialog.dart

@@ -0,0 +1,49 @@
+import 'package:flutter/material.dart';
+
+/// A custom dialog that makes the title bold, puts the actions in a column, and adds a subtle border.
+class FrostyDialog extends StatelessWidget {
+  final String title;
+  final Widget content;
+  final List<Widget>? actions;
+
+  const FrostyDialog({
+    Key? key,
+    this.actions,
+    required this.title,
+    required this.content,
+  }) : super(key: key);
+
+  @override
+  Widget build(BuildContext context) {
+    return AlertDialog(
+      titlePadding: const EdgeInsets.all(30.0),
+      contentPadding: const EdgeInsets.fromLTRB(30.0, 0.0, 30.0, 30.0),
+      shape: RoundedRectangleBorder(
+        side: BorderSide(
+          color: Colors.deepPurpleAccent.withOpacity(0.3),
+          width: 3.0,
+        ),
+        borderRadius: BorderRadius.circular(20.0),
+      ),
+      title: Text(
+        title,
+        style: const TextStyle(fontWeight: FontWeight.bold),
+      ),
+      content: SingleChildScrollView(
+        child: Column(children: [
+          content,
+          if (actions != null) ...[
+            const SizedBox(height: 20.0),
+            ...?actions?.map(
+              (action) => Container(
+                width: double.infinity,
+                padding: const EdgeInsets.only(top: 10.0),
+                child: action,
+              ),
+            ),
+          ],
+        ]),
+      ),
+    );
+  }
+}