Console script updates and driver updates

[mdmintz]

• You can now install web drivers by using seleniumbase console scripts:

seleniumbase install chromedriver
seleniumbase install geckodriver
seleniumbase install edgedriver

(SeleniumBase takes care of determining the latest version for your operating system's platform, downloading the zip file, extracting the driver from the zip file to the SeleniumBase drivers/ folder, and setting the permissions of the driver with "chmod" to make it executable for browser tests.)

• You can now run tests in headless mode without using pyvirtualdisplay.
  Usage: --headless. (Make sure you have the latest versions of Chrome and Firefox installed.)

pytest my_first_test.py --browser=chrome --headless