Added ScriptBox element

ScriptBox() class added for customization template page
Added some extra logging for flash messages
Added page_controls_exist() method
Simple docs fix
Added entire suite of page models for PXE

* PXEServer()
* CustomizationTemplate()
* SystemImageType()
Added tests for PXE

* Added PXE Server CRUD tests
* Added Customization Template CRUD tests
* Added System Image Type CRUD tests
* Added RHEL template file
Merge pull request #615 from psav/pxe_objects_and_tests

PXE objects and tests