Initiative – fill typescript types everywhere

[zbycz]

This project is becoming more mature, and allowing any in function calls etc makes bugs easier.

We can force types by lint rules eg in core parts like services and FeaturePanel first.

Next step is alowing typescript strict mode, which also need undefined to be explicitly specified (currently any type can be undefined/null), which will also help in thinking about dataflows.

It would be benefical to create (small) pull request only with adding types. If possible.

• add types to fetchJson #599