Define a concept how to store types of never explored actions

[tdauth]

For more complex strategies like ToStateWithUnexploredActions in the legacy code, we need to know which actions have not been explored in all states.
Note that we cannot really limit actions such as ChangeValueOfAction because we have to fill them with random values.
Hence, it would make more sense to store types of never explored actions together with the XPath of the target element.
Note that these never explored action types must be passed when getting a state like in the legacy API.

[tdauth]

The action type is only part of Surili. Surili can get the types from the concrete actions. The state graph can store a counter of unexplored action types only. This counter has to be set once the state is created.

Maybe we should distinguish between:

createState(sutState : SutState, neverExploredActionTypesCounter : Int) : State
getState(sutState : SutState) : Option[State]

The counter should be decreased whenever an unexplored action is executed?