Add proper mime type to shared gpx files

This prevents apps to show up in the intent chooser that do not know how
to deal with gpx files (e.g. Conversations)

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/activities/ActivitySummariesActivity.java

@@ -273,7 +273,7 @@ public class ActivitySummariesActivity extends AbstractListActivity<BaseActivity
 
         if(uris.size() > 0) {
             final Intent intent = new Intent(Intent.ACTION_SEND_MULTIPLE);
-            intent.setType("*/*");
+            intent.setType("application/gpx+xml");
             intent.putParcelableArrayListExtra(Intent.EXTRA_STREAM, uris);
             startActivity(Intent.createChooser(intent, "SHARE"));
         } else {