THUCYDIDES-173 use either locale to format string or default to US

Uses 2 strategies:
WhenObtainingResultSummariesFromTestOutcomes and WhenFormattingForHTML => we force the use of US locale (we are checking the formatter, so we use any locale (US) and verify the string)
WhenCalculatingStoryCoverage => we compare result using the current Locale (we got the result from the webbrowser and we want to check the value is accurate, not that it specifically match any locale)

with this, the tests are passing independently of the locale used by the machine running the test.
To modify the current locale, use java user.country and user.language, either using argLine with maven or passing it to the jvm when running test in an IDE