Renamed the options specific to the TIFF handler.

The loading/saving options that are specific for TIFF were in the form of wxIMAGE_OPTION_<name> while all other non-generic options use the form wxIMAGE_OPTION_<imagetype>_<name>. Renamed the TIFF options to the form wxIMAGE_OPTION_TIFF_<name> and kept the old names for backwards compatibility.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68780 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775