use alert state changes counter for alert notification dedupping.

If notification state is pending and last update of state was made
less than a minute ago. In the case of a grafana instance is shut down/crashes
between setting pending state and before sending the notification/marks as complete
this logic should allow the notification to be sent after some time instead of
being left in an inconsistent state where no notifications are being sent.

Grafana high availability (ha) test setup

Adding AWS Isolated Regions

Plugin list to react

Compile TS on precommit hook

- was not covered by TS lint
- TS errors are only noticed in broken builds
- added grunt task to run `tsc --noEmit`

Merge branch 'text_variable-3173' of https://github.com/daldoyle/grafana into daldoyle-text_variable-3173

fixes to dark theme for Explore mode