Update app launcher icons and first name label.

Replaced launcher icon assets for all mipmap densities (hdpi/mdpi/xhdpi/xxhdpi/xxxhdpi). Also updated the sign-up screen first name field hint and label from "User Name" to "User First Name" in sign_up_screen_step1_view.dart for clearer UX.

lib/app/modules/sign_up/views/sign_up_screen_step1_view.dart

@@ -67,10 +67,10 @@ class SignUpScreenStep1View extends GetView<SignUpScreenStep1Controller> {
                       enableInteractiveSelection: false,
                       refKey: FormFieldConstants.instance().getFormKey("${className}firstNameField"),
                       controller: FormFieldConstants.instance().getController("${className}firstNameField"),
-                      hintText: "User Name",
+                      hintText: "User First Name",
-                      labelText: TranslationKeys.makeTranslation("User Name"),
+                      labelText: TranslationKeys.makeTranslation("User First Name"),
                       inputFormatters: [LengthLimitingTextInputFormatter(FieldUtils.userNameFieldLength)],
-                    ),
+                    )
                   ),
                   const Spacer(),
                   Expanded(