Queue tasks

[tomzx]

When launching the CLI, it should be possible to specify a sequence of tasks to execute sequentially (maybe a graph of tasks?).

For instance, we currently have SummarizeMultiplePersonas as a task, which is in itself a collection of calls to Simple, followed by a SummarizeResponses.

In #36 we want to implement a personas selector. The idea would be to run SelectPersonas, then QueryMultiplePersonas with the returned list, and finally SummarizeResponses.

We should be able to get rid of SummarizeMultiplePersonas and replace it with QueryMultiplePersonas,SummarizeResponses.

The goal is to increase reusability while reducing the need for tasks that are composite of other tasks.