Stealth Alert

v1.4.0

New detections
- Hyper-Vision Goggles (item 23763 / spell 30249) - Engineering helm, grants the stealth
  detection of a character 6 levels higher for 15s. Shown in orange with the remaining duration.
  Thanks for the request!
- Elixir of the Searching Eye (item 22830 / spell 28496) - +15 stealth detection for 10 min.
  Found while checking the request above; arguably the bigger threat of the two, since it lasts
  a full 10 minutes.

That brings StealthAlert to 6 detected threats : Perception, Felhunter, Catseye Elixir,
Hyper-Vision Goggles, Searching Eye, Track Hidden.

Improvements
- Timers longer than a minute now display as `m:ss` instead of raw seconds (the Searching Eye
  buff used to read "600s").
- Threat display can hold more simultaneous alerts, and the options panel was resized to fit
  the updated threat list.

A note on passive gear
Items with a permanent equip bonus - Bloodvine Lens, The Night Watchman, Catseye Ultra
Goggles, PvP Dragonhide gloves - apply spell 23217, which is flagged Aura is hidden and
No Aura Icon. The client cannot read it through `UnitBuff`, so no addon can alert on those.
Only activated effects (racials, elixirs, goggles on-use) are detectable.

Also worth clarifying since the names are confusing: Ultra-Spectropic Detection Goggles
(item 23762) grant gas cloud tracking and long-distance zoom - no stealth detection at all -
so there is nothing to detect there.