lokdocview: move callback handling to LOKDocView_Impl
lokdocview: move callback handling to LOKDocView_Impl

These were the last free functions that passed around a LOKDocView_Impl*
manually just because it was not possible to have them in a C++ class
when lokdocview was C code.

Change-Id: I6229a853336db0e47f7d1ba4687d198e076934a3

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core