added zclip offset to gfx objects

modules/gfx/pymod/export_gfx_obj.cc

modules/gfx/src/gfx_object.cc

modules/gfx/src/gfx_object.hh

modules/gfx/src/gfx_object_base.hh

modules/gfx/src/shader/basic_fs.glsl

modules/gfx/src/shader/dumpnorm_fs.glsl

modules/gfx/src/shader/fraglight_fs.glsl

modules/gfx/src/shader/fraglight_vs.glsl

modules/gfx/src/vertex_array.cc

modules/gfx/src/vertex_array.hh