Zotlabs: Improve type safety for AccessList class.

Add type annotations for constructor and set* methods, and throw an exception if the passed in arrays are missing required keys. This means that both invalid input types and missing keys will throw and exception rather than just die with a runtime error.

There's not checks to verify that the contents of the required array keys are valid or make sense, though. They are just assigned, and returned as is by the get method when requested.

Also, the set_from_array method is not well tested at the moment.