add prettier for code styles (1.)

[simllll]

this is the first PR, needs to be merged first before applying lib updates & co

To keep discussion short, I just added prettier (https://prettier.io/) It's a well known code style formatter, which has almost no configurations. Therefore it should be good to go ;).

This one is very handy for all future git commits/PRs and so on. Please consider it to merge soon. No Code change, only code formatted with prettier.