Update to Typescript 3.8

[dvvanessastoiber]

Observed behavior

Updating the typescript and typedoc versions according to the snippet below without using stricter linting makes it possible to use the current typescript version with a minimum amount of errors.

"typedoc": "~0.16.9",
"typescript": "~3.8.1-rc",

Expected behavior

Updating the dependencies in the package.json and adding the following line of code in tsconfig.json (as well as fixing appearing type errors) should be sufficient for the usage of Typescript 3.8 as a first step.

"downlevelIteration": true, // required as long as target is `es5`