This series moves several common key bindings into a shared notmuch-wide keymap. To get there, it first cleans up several things so that all notmuch modes have common commands to put into a common keymap. In the process, this fixes inconsistent sort ordering reported in id:m2bo5c5h8l.fsf@ramakrmu-mac.i-did-not-set--mail-host-address--so-tickle-me, improves the currently fragile hello refresh behavior, combines several mostly-duplicated commands, and improves the notmuch-help implementation. This passes all of the tests and basic interactive testing, but it would be good for people to exercise it.