Feature/rb 82 notification component

[pratibha-growexxer]

• [x] Design Notification Component with drop-down
• [x] Mark notifications as read.
• [x] Notification unread count.
• [x] Skeleton Loader for loading.
• [x] Infinite Scrolling for more lists.
• [x] Doc update.
• [x] Test cases.

NOTE: Refactored cart logic written in notification component. Made one new component for Cart.

• PR can be merged in master.