title: Active_shipping Fedex API Authentication Error
body: <p>I'm implementing aсtive_shipping plugin functionality in my app. I've got test account from fedex and trying to get some shipping rates as shown in plugin's readme at github:</p>
  
  <pre><code>fedex = FedEx.new(:login =&gt; '***', :password =&gt; '***', :key =&gt; '***', 
  :account =&gt; '510087569', :meter =&gt; '100054531')
  response = fedex.find_rates(origin, destination, packages)
  </code></pre>
  
  <p>This request causes an error: <code>ActiveMerchant::Shipping::ResponseError (ERROR - 1000: Authentication Failed)</code></p>
  
  <p>Also I'm confused with all that APIs keys (DHL, UPS etc). Can I use same account keys in different apps for each of carriers or should I make new ones for every app?</p>