Use new labels

We've got new labels in gracedb now (see computing/gracedb/server!116 (merged)), so now we need to use them. Specifically, swap out EM_Selected and EM_SelectedConfident with LOW_SIGNIF_LOCKED and SIGNIF_LOCKED respectively, and add LOW_SIGNIF_PRELIM_SENT.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information