Storing Tasks locally for access without network.

## Description
As an user of the app, sometimes I may need to check my task list but network connection may not be available. So my tasks should be stored locally in my phone. For example in Whatsapp, you can check the chats even if you're offline. In the same way, I should be able to check my stats on the app without going online. We can use room database for storing the data locally.

## Acceptance Criteria
### Update [Required]
- [ ] [The data is stored and made available to the user even when offline. (Task list only)

## Definition of Done
- [ ] All of the required items are completed.
- [ ] Approval by 1 mentor.

## Estimation
2-4 hours depending on fluency with the backend and database.