Inline and mark as deprecated images's serialNumber()

Inline and mark as deprecated images's serialNumber()

These function are marked as obsolete since Qt 4.3

The motivation here was too fix QPixmap::serialNumber which is marked as
QT_DEPRECATED_SINCE but was not inlined.
But then I took the oportunity to do the same with all the other
functions.

Change-Id: Ic50a7857461fc402b2f2b4528c83e53e8e28ea30
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>