JITB-41: Transition from "pure success" to a bit of "best effort"

[hark130]

Improved all four legacy JbgAbc child classes more robust by improving vote_answers() and write_an_answer().

Fixed jitb_webdriver.click_a_button()

• Moved Exception-raising reference inside try/except
• Added debug logging if a button match wasn't found

Made get_prompt() more robust by catching StaleElement exceptions.