Put AMBER99SBildn into SMIRNOFF format

[davidlmobley]

@cbayly13 and I have tentative plans to put AMBER99SB-ildn into SMIRNOFF format. We don't think it should be that hard given all the work he already did on parm99; the tentative plan is for him to do parm99 and then me to do the -ildn extensions (which are only ~200 lines).