Restrict walking mode changed broadcast to package

Fixes potential privacy leak and lint error:

/home/runner/work/privacy-friendly-pedometer/privacy-friendly-pedometer/app/src/main/java/org/secuso/privacyfriendlyactivitytracker/persistence/WalkingModePersistenceHelper.java:152:
Error: The intent action
org.secuso.privacyfriendlystepcounter.WALKING_MODE_CHANGED (used to send
a broadcast) matches the intent filter of a non-exported component
org.secuso.privacyfriendlyactivitytracker.receivers.StepCountPersistenceReceiver
from a manifest. If you are trying to invoke this specific component via
the action then you should make the intent explicit by calling
Intent.set{Component,Class,ClassName}. [UnsafeImplicitIntentLaunch]
Intent localIntent = new
Intent(BROADCAST_ACTION_WALKING_MODE_CHANGED);

app/src/main/java/org/secuso/privacyfriendlyactivitytracker/persistence/WalkingModePersistenceHelper.java

@@ -150,6 +150,7 @@ public static boolean setActiveMode(WalkingMode mode, Context context) {
         boolean success = save(mode, context).isActive();
         // broadcast the event
         Intent localIntent = new Intent(BROADCAST_ACTION_WALKING_MODE_CHANGED);
+        localIntent.setPackage(context.getApplicationContext().getPackageName());
         localIntent.addFlags(Intent.FLAG_INCLUDE_STOPPED_PACKAGES);
         if (currentActiveMode != null) {
             localIntent.putExtra(BROADCAST_EXTRA_OLD_WALKING_MODE, currentActiveMode.getId());