Fix typing in SDK functions

[stavrostheocharis]

Description There is a need to change the typing in some functions

Solution

• dict should be Dict with additional parts inside eg. Dict[str, float]
• In some parts that None is returned or None is default, Union should be used to include the None value

[momegas]

Related to #139

[sinnec]

I think some further reading should be done about the return dict types: https://stackoverflow.com/questions/51291722/define-a-jsonable-type-using-mypy-pep-526