Add runtime type checks for config

[podliashanyk]

With TS, type guards can not be applied at runtime for optional config values. Thus when values of incorrect types are provided in runtime-config.json, the app does not work as expected.

Suggested solution
Show error message if config is provided with values of incorrect types.. Add user defined type guards to config.tsx. F.e. as described here https://stackoverflow.com/a/43279180

Depends on #536 being merged.

[podliashanyk]

Setting low prio since expected formats of config values are documented in #536, so this shouldnt be a serious issue