Save task data in solution

[juztamau5]

This saves the task data alongside the solution. For example, a logging service could reproduce individual steps of the solution.

Before:

{
  "solution": "0x0000000000000000000000000000000000000000000000000000000000000024",
  "finalized": true
}

After:

{
  "solution": "0x0000000000000000000000000000000000000000000000000000000000000024",
  "finalized": true,
  "data": [
    1,2,3,4,5,6,7,8,9
  ]
}

Requires #6.