WalletApplication: Use SystemClock.elapsedRealtime() to detect reboot

This will replace using BootstrapReceiver which comes with a delay in
receiving the reboot notice.

wallet/src/de/schildbach/wallet/WalletApplication.java

@@ -67,6 +67,7 @@
 import android.net.Uri;
 import android.os.Build;
 import android.os.StrictMode;
+import android.os.SystemClock;
 import android.preference.PreferenceManager;
 import android.support.annotation.StringRes;
 import android.support.multidex.MultiDexApplication;
@@ -632,7 +633,9 @@ else if (lastUsedAgo < Constants.LAST_USAGE_THRESHOLD_RECENTLY_MS)
 
     public void lockWalletIfNeeded() {
         WalletLock walletLock = WalletLock.getInstance();
-        if (walletLock.isWalletLocked(wallet)) {
+        boolean recentReboot = SystemClock.elapsedRealtime() < WalletLock.DEFAULT_LOCK_TIMER_MILLIS &&
+                config.getLastUnlockTime() < (System.currentTimeMillis() - SystemClock.elapsedRealtime());
+        if (walletLock.isWalletLocked(wallet) || recentReboot) {
             walletLock.setWalletLocked(true);
         }
     }
@@ -675,10 +678,4 @@ public void killAllActivities() {
         AbstractWalletActivity.finishAll(this);
     }
 
-    public static void resetWalletLockTimer(final Context context) {
-        final Configuration config = new Configuration(PreferenceManager.getDefaultSharedPreferences(context),
-                context.getResources());
-        config.setLastUnlockTime(0);
-    }
-
 }

wallet/src/de/schildbach/wallet/service/BootstrapReceiver.java

@@ -56,8 +56,6 @@ public void onReceive(final Context context, final Intent intent) {
             if (config.remindBalance() && config.hasBeenUsed()
                     && config.getLastUsedAgo() > Constants.LAST_USAGE_THRESHOLD_INACTIVE_MS)
                 InactivityNotificationService.startMaybeShowNotification(context);
-
-            WalletApplication.resetWalletLockTimer(context);
         }
     }
 }