Add Qt5 support

PythonQt_QT_VERSION cmake option is added ("4" or "5"). If "5",
PythonQt_Wrap_QtXYZ use a XYZ with the same Qt5 casing, if "4" it is lower
case, e.g. PythonQt_Wrap_QtWebKit vs PythonQt_Wrap_Qtwebkit

To be done:
* Rebase Qt5 support on PythonQt trunk (some changes in this commit
(e.g. in PythonQt.cpp) might not be due to a Qt5 support)
* Fix XmlPatterns
* Split generated_cpp folders regarding to Qt modules.
* Remove findCharOffset() and use QByteArray methods instead
* Bonus: Factorize method signature processings
* Fix warning:
src/PythonQtConversion.cpp: In static member function ‘static QVariant PythonQtConv::PyObjToQVariant(PyObject*, int)’:
src/PythonQtConversion.cpp:1044:27: warning: deprecated conversion from string constant to ‘char*’ [-Wwrite-strings]

Based on Melven Zöllner work (
http://sourceforge.net/p/pythonqt/discussion/631392/thread/5f20c176/)