SystemChecker methods should return more organized data

[firaja]

Each method of SystemChecker class returns an int, but for algorithm like Argon2 there is the need to return both the number of iterations and memory, since memory must be lowered if the minimum execution time required cannot be met.^{See Section 9}

It could return a prototype of the function.

Result result = SystemCheker.find...(...)

result.getPrototype() // instance of AbstractHashingFunction
result.getElapsed() // this may be not equal to the desired minimum computational time