kbfsedits: implement a user history object
kbfsedits: implement a user history object

Sort individual TLF histories by last modified time, and convert
individual TLF histories into keybase1 protocol data structures.

Issue: KBFS-2996

keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client