Returned plans should be parsed and returned in a well structured way; plan cost including

Some planners return their entire diarrheas output into the `result.output.plan` field. Some return a properly formatted plan as text. The original `/solve` interface returned the plan in a rich Json structure. The planutils should be able to parse and standardize the plan structure between temporal and strips planners.

The plan cost is also included in different formats in the planner output. With bit of luck, one can get the plan from `result.output.plan` field and find the cost from the `result.stdout`. But as soon as you have multiple plans, you cannot figure out what belongs to what.

Ideally, `result.output.plan` should be a structured element with `steps` or `actions` if you want as well as `cost` and/or `makespan` and possibly the search stats such as `statesEvaluated`.