Consider creating helper functions for common puppeteer commands

[austinkelleher]

It may become tedious to constantly call window.puppeteerCommand(...). We could implement helper functions for common commands such as screenshot, goto etc.

My main concern is with this is that it may be confusing for people that only certain functions are exposed.

Thoughts @charlieduong94?

[ctdio]

Exposing a few helper functions would be nice to have. I'm in favor of possibly deprecating window.puppeteerCommand (or maybe marking it as unsafe) and exposing only a small subset of commands. Commands such as goto can be harmful since it causes the current page to redirect, thus causing the test suite to stop.