Use one script engine and one script debugger to avoid slow down of the skin parsing 

+ Using the debugger is much faster than before
+ The debugger is disabled on the spinny widget to avoid segfault (multithread?).
+ The global object is preserved from a skin context to it's children (as when there is one scriptEngine per context).
+ The translation js api is enabled (http://qt-project.org/doc/qt-4.8/qscriptengine.html#installTranslatorFunctions)
+ Removal of a circular reference of the global object in the svg extension 

I have a really fast SSD here so I didn't realize the slow down was so massive. Please tell me if there is another bottleneck on different setups.
This should probably return the QSharedPointer so that callers don't steal the bare pointer without a reference count.