Move FBX importer's Cycles material 'convertor' to modules.

That way other addons may use it as well.

io_scene_fbx/import_fbx.py

@@ -1292,7 +1292,7 @@ def blen_read_material(fbx_tmpl, fbx_obj, settings):
     ma_refl_color = elem_props_get_color_rgb(fbx_props, b'ReflectionColor', const_color_white)
 
     if settings.use_cycles:
-        from . import cycles_shader_compat
+        from modules import cycles_shader_compat
         # viewport color
         ma.diffuse_color = ma_diff