WIP #3238 - user sets gap for srw export
WIP #3238 - user sets gap for srw export

radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,mkeilman/sirepo,radiasoft/sirepo,radiasoft/sirepo,mkeilman/sirepo,mkeilman/sirepo