Scenario option to customize initial view center

[byorgey]

Is your feature request related to a problem? Please describe.
By default, the view always starts out centered on the base robot. But if the base robot is not centered in the map, this can mean that part of the map is off the screen. Of course the user can always scroll the map (unless explicitly disabled) but for scenario design it would be nice to have the option to specify where the view is centered. This would also mean that for such scenarios the view would not follow the base robot as it moves around (unless the player explicitly recentered the view on the base).

Describe the solution you'd like
A new optional viewcenter field under world which takes either a robot name or a location tuple.

[byorgey]

Concretely, we could move the definition of the ViewCenterRule type to the swarm-scenario library, and include a field with this type in PWorldDescription.

[byorgey]

A few reasons this is trickier than I thought:

• In the specification of a world we will want to specify a robot to view by name, whereas at runtime it should be specified by RID.
• There can be many world specifications in a scenario (a default world + subworlds), and each one could have its own view center rule.