Merge pull request #212 from indikasampath2000/performance

Tracking data removing logic re-write in SlotDeliveryWorker
Fix for ContentRemovalTask concurrent modification issue :beetle:

Replaced synchronised ArrayList with a ConcurrentHashMap
Merge pull request #213 from Asitha/content-removal-task

Fix for ContentRemovalTask concurrent modification issue
Some of tracking data not removing issue fixed and trace logs added