Improve the lockdown intervention

[akshaydewan]

These are some points we have discussed that need to be refined, prioritized, and split into individual issues.

1. If the number of infections remains over the defined threshold, the lockdown intervention gets re-applied immediately the next simulation day. We should extend the lockdown instead of lifting it.
2. Introduce the concept of "detected" cases which will drive the lockdown, rather than the total number of infections. (This will have implications and dependencies on other features too).
3. We can potentially allow a few inter-region transports (for essential services) during the lockdown. (Maybe a lockdown can have different levels - normal lockdown, sealed etc.)
4. Instead of lifting the lockdown outright, it can be lifted in a phased manner - allowing a percentage of the population to work and maintaining lesser density in workplaces.

[akshaydewan]

Point 1 has been covered in https://github.com/thoughtworks/epirust/commit/777135f05a595da2034ae43de43f99882c2d28a3