Allow passing named parameters to testAction function

testAction has too many parameters. This allows it to be used with named args instead (using a single object). Update in backwards-compat way (I hope!) so we don't need to replace old instances right now.

Usage examples:

before (thought-process comments added for emphasis):

testAction(
  actions.fetchIssuesForList,               // ok this is action so far so good
  { listId },                               // initial state I guess?
  {},                                       // ?? oh wait this is actually state. Previous param must be payload
  [{                                        // ???
    type: types.REQUEST_ISSUES_FOR_LIST,    // oh ok this is expected mutations
    payload: { listId, fetchNext: false }   // this is fine
  }],
  [],                                       // ???
  done,                                     // I hope I added enough empty arrays
);

after:

testAction({
  action: actions.moveList,
  payload: { listId },
  expectedMutations: [{
    type: types.REQUEST_ISSUES_FOR_LIST,
    payload: { listId, fetchNext: false },
  }],
  done,
});