This adds prettier to the repo, and sets up the pre-commit hook to
auto-format as well as lint.
Also updates ignores files to exclude crawls, test-crawls, scratch, dist as needed.
* ad blocking via request interception, extending block rules system, adding new AdBlockRules
* Load list of hosts to block from https://raw.githubusercontent.com/StevenBlack/hosts/master/hosts added as json on image build
* Enabled via --blockAds and setting a custom message via --adBlockMessage
* new test to check for ad blocking
* Add test-crawls dir to .gitignore and .dockerignore
