Small bugs fixes

Hi there's few more small updates.

* moved forgotten test to appropriate place
* now you actually can create TicketSearchRequest ("where()" method wasn't static)
* added escaping non xml valid in kayako response

Last issue was quite unexpected for me. I've got some tickets in my system with broken encoding in some parts of the message.
Kayako wrap all user generated content in CDATA sections, but according to XML specification not every symbol still valid even wriped in CDATA. So XML unmarshaler was throwing exceptions on this special symbols. Now they just filtered out from response (mainly symbols with hex codes lower then 0x20)