Add Q_DECL_OVERRIDE in the src subdirectory

Done automatically with clang-modernize on linux

(But does not add Q_DECL_OVERRIDE to the function that are marked
 as inline because it a compilation error with MSVC2010)

Change-Id: I2196ee26e3e6fe20816834ecea5ea389eeab3171
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>