Nested payload groups

[patinthehat]

I'd like to see the ability to group messages that are sent to Ray, similar to the way that console.group() and console.groupEnd() work:

I know the colors can be used for grouping, but I feel that something like this would be very useful - especially if the groups can be nested and collapsed/expanded.

This would likely mean some not-insignificant changes to the way payloads are created on both the client side and handled server side - I'm willing to work on the client side code if this is something you decide to implement.

Thoughts?

This discussion is similar to #214.