Make EasyPost USPS account configurable

source/static/makeshipment.php

@@ -55,7 +55,7 @@ try {
                 "weight" => 3.5
     ]);
 
-    $shipmentinfo["carrier_accounts"] = ["ca_fe31a7e4fcf24438b8cdfb74541c7094"]; // USPS
+    $shipmentinfo["carrier_accounts"] = [$_SETTINGS["easypost_usps_account"]]; // USPS
 
     if ($_REQUEST["postagetype"] == "certified") {
         $shipmentinfo["options"]["certified_mail"] = true;

source/static/settings.sample.php

@@ -4,6 +4,7 @@ $_SETTINGS = [
     "debug" => false,
     "easypost_key" => "",
     "stripe_sk" => "",
+    "easypost_usps_account" => "ca_9...b5",
     "email" => [
         "server" => "mail.netsyms.net",
         "port" => 587,