extra form validation and connection list done

lib/connection.dart

@@ -0,0 +1,44 @@
+import 'dart:convert';
+
+class Connection {
+  String? host;
+  int? port;
+  String? username;
+  String? privateKey;
+  String? password;
+  bool? isEncryptionEnabled;
+  bool? isDefault;
+
+  Connection() : isEncryptionEnabled = true, isDefault = false;
+
+  Connection.fromJson(Map<String, dynamic> json) {
+    host = json['host'];
+    port = json['port'];
+    username = json['username'];
+    privateKey = json['privateKeyFilePath'];
+    password = json['password'];
+    isEncryptionEnabled = json['isEncryptionEnabled'];
+    isDefault = json['isDefault'];
+  }
+
+  String get toJson => jsonEncode({
+    'host': host,
+    'port': port,
+    'username': username,
+    'privateKeyFilePath': privateKey,
+    'password': password,
+    'isEncryptionEnabled': isEncryptionEnabled,
+    'isDefault': isDefault
+  });
+
+
+  bool assertComplete() {
+    assert(host != null);
+    assert(port != null);
+    assert(username != null);
+    assert(privateKey != null || password != null);
+    assert(isEncryptionEnabled != null);
+    assert(isDefault != null);
+    return true;
+  }
+}