Keep alarm notification on screen

If the user picks up their phone late while the alarm
is going, they might not realise the controls are in
the notification not the app.

Closes #75

android/app/src/main/AndroidManifest.xml

@@ -6,6 +6,7 @@
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.REQUEST_IGNORE_BATTERY_OPTIMIZATIONS" />
+    <uses-permission android:name="android.permission.USE_FULL_SCREEN_INTENT" />
     <uses-permission tools:node="remove" android:name="android.permission.ACCESS_NETWORK_STATE" />
 
     <application

android/app/src/main/java/com/massive/TimerService.kt

@@ -80,10 +80,10 @@ class TimerService() : Service() {
                         PendingIntent.FLAG_IMMUTABLE
                     )
                 builder.setContentText("Timer finished.")
-                    .setAutoCancel(true)
                     .setProgress(0, 0, false)
-                    .setOngoing(false)
-                    .setContentIntent(finishPending)
+                    .setAutoCancel(true)
+                    .setOngoing(true)
+                    .setFullScreenIntent(finishPending, true)
                     .setChannelId(CHANNEL_ID_DONE)
                     .setCategory(NotificationCompat.CATEGORY_ALARM)
                     .setDeleteIntent(pendingStop)