WTBSummonINV

- **Picking a location while grouped now announces it instead of blocking.**
  Previously, if you were already in a group or raid, picking a location just
  warned you to leave first. But if you're already in the *summoner's* raid,
  that's wrong - you just need to call out the destination. The addon can't tell
  one raid from another without extra weight, so it now does the useful thing for
  both cases: it posts the location to raid/party chat **and** prints a short
  chat note (no alarm sound or screen flash - it fires on every repeat summon). If
  you're in the summoner's raid you're set (disregard the note); if you're in a
  different group, it tells you to leave and pick again.
- Shortened the auto-accept invite window from 45 to 15 seconds, so a stray
  group invite is less likely to be caught while you're waiting for the summoner.

- **No more automatic `/who` at login.** The addon no longer searches for
  summoners when you log in, so logging in never colours the button or pings the
  server on its own. The status check now runs only when you ask for it:
  shift-click the minimap button (or `/wtbsummon status`), or any left-click that
  requests a summon. Left-click and the right-click location list are unchanged.
- Dropped the "Check status automatically at login" option and the
  `/wtbsummon login` command that went with it.