feat: a Not spam action

Backlog item 201. A message in the Spam view had no way back out: spam is
one-way and Restore is hidden outside the trash. not_spam moves each message
to the folder its moved-from: origin names, falling back to the account's
inbox (reported) for provider-caught mail with no origin.

The action is labelled "Not junk" on the free Alt+J: every letter of "Not
spam" is taken in the Message menu, and Alt+P (Re&ply) and Alt+S (Mark &spam,
frozen) are unavailable.

restoreResolvedMessages() and the undelete_thread branch are parameterised
with the cleared tag and undo description rather than copied, so Delete and
Not spam cannot drift.

0 files changed, 0 insertions, 0 deletions