Implement VM Status Monitoring and Alerts

[zaelgohary]

Is your feature request related to a problem? Please describe

As a user, I'd like to know if any of my contracts went in grace period.

[zaelgohary]

WIP:

Added contract check service but not added to notifications page.

[zaelgohary]

WIP:

Edited notification service settings. Added contract notifications toggle to the notifications page. Tested the contract check service and edited main.dart to run backgroundFetchHeadlessTask instead of checkNodeStatus. Removed finishing task logic inside the background service itself.

Now, for some reason, the node check service sometimes returns an empty array and throws the following err:

Still investigating why.

[zaelgohary]

Work Completed:

After some research, I found that a timeout might happen from the OS for the background task for multiple reasons. I fixed some bugs and edited dialogue style. Also, added a button to trigger notifications manually just for testing purpose. Will be removed before merging the PR.