Convert unit tests from TS to JS

[christroutner]

There are issues with using TS to write unit tests. Here is an example of why unit tests should be written in JS:

I couldn't write a test-case to test the error handling if a user passes a string in place of an integer, because that test case invalidates the typings in TS. But the fact is that anyone can import the bitbox-sdk library into a JS project and they can accidentally pass a string in place of an integer.

So here is a case in which we can't even write a test because of TS, to catch a very real use case.