NX Sentry 0.2.1

Two fixes found reviewing the 0.2.0 work.

• The tray kept claiming motion. An alarm that timed out into its quiet time
  never told the main process, so the tray icon, its tooltip and its enabled
  "Silence alarm" item stayed on "Motion detected" until the next manual arm or
  disarm. Every transition is reported now.
• The meter froze while you dragged the sensitivity slider. Any settings
  change rebuilt the sample timer, and a drag resets it faster than it can fire —
  so the live reading stopped exactly when you were watching it to pick a
  threshold. Only the sample rate touches the timer now.

The detection panel also shows what a sample actually costs, and turns amber
when one no longer fits inside its own interval — pixel-exact analysis is linear
in the region's area, and an overrunning sample starves the UI instead of
reporting anything.