fix(timers): keep a ramp from restarting mid-ring and a migration from guessing

A timer ring that hands over from one expired timer to another now starts at full volume instead of ramping again from near silence.

The timer-vibrate migration only treats an install as fresh when the package was never updated and the store is empty. An updated install whose store was replaced after corruption, or an Auto Backup restore onto a new device, keeps the alarm default as before.

The Vibrate row now says whether it is on, and only when it is off adds that a silent timer still vibrates.

Refs #22

app/src/main/res/values/strings.xml

@@ -300,7 +300,7 @@
     <string name="settings_section_timers">Timers</string>
     <string name="settings_timers_subtitle">Sound, vibration and gradual volume</string>
     <string name="settings_timer_defaults_hint">How timers ring. A timer can still pick its own sound in its editor.</string>
-    <string name="settings_timer_vibrate_hint">A timer set to silent vibrates either way</string>
+    <string name="settings_timer_vibrate_off">Off. A timer set to Silent still vibrates</string>
     <string name="settings_section_clock">Clock</string>
     <string name="settings_clock_subtitle">Home time zone</string>
     <string name="settings_clock_hint">World clocks show how far each city is from your home time zone.</string>