[APPS-392] No longer escaping XML content before sending over to Freshbooks

It looks like Freshbooks may have changed their API to no longer accept escaped XML. Removing the escaping (which is what this PR does) immediately alleviates the problem described below

> Freshbooks app returns error when looking up users: 
> ![](http://f.cl.ly/items/0i3x2E0G451r1q0C3i2Z/Screen%20Shot%202013-03-14%20at%2011.43.03%20AM.png)
>
> That error was caused by the Freshbooks API returning this on all our calls:
>
> ```
> <?xml version="1.0" encoding="utf-8"?>
> <response xmlns="http://www.freshbooks.com/api/" status="fail">
>   <error>Your XML is not formatted correctly.</error>
>   <code>40010</code>
> </response>
> ```