Background Task bug fix

[rafsanulhasan]

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[x] Feature
[ ] Code style update (formatting)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[x] Other..:
     - Toast UI improvement
     - Fixed unexpected cancellation of background task
     - Nicely designed Toasts for **error messages**

What is the current behavior?

[ ] unexpected crash [ ] abnormal behavior [ ] unexpected cancellation of background task

What is the new behavior?

• [x] Newly designed toast
• [x] Navigating on ManPage and Notifications page trigger background task
• [x] Clicking on the toast opens proper page on the app
• Clicking on Mark as Read button on the toast will do the following in the background when the app is running
  • [x] Marks the specific notification as read
  • [x] Updates ViewModel with newly fetched Unread notifications in the background
  • [x] Send Message to all views and viewmodels
  • Reflects Data updates in the app
  • [x] Updates the notification indicator on the mainview
  • [x] Reflects updated data in the unread tab of notifications view
  • Merge toasts
  • [x] Read notifications will be removed from toast and newly arrived notifications will be shows in the toast.
• [x] When the app is open it syncs at a 15 min delay for new notifications and merges them with the toasts and Send a signal to all the viewmodels with proper message types that would reflect in the mainview and notifications view as well.

Does this PR introduce a breaking change?

[x] Yes
[ ] No

Other information

[aalok05]

Great work @rafsanulhasan !