change blender python interface for classes not to ise __idname__ rather bl_idname since __somename__ is for pythons internal use.

replacements...
"__idname__" -> "bl_idname"
"__props__" -> "bl_props"
"__label__" -> "bl_label"
"__register__" -> "bl_register"
"__undo__" -> "bl_undo"
"__space_type__" -> "bl_space_type"
"__default_closed__" -> "bl_default_closed"
"__region_type__" -> "bl_region_type"
"__context__" -> "bl_context"
"__show_header__" -> "bl_show_header"
"__URL__" -> "_url"