Improved Windows detection

[roccozanni]

In some cases, the os parser was incorrectly producing a os string containing also the Windows version. For example, with iTunes user agent strings like this one:

iTunes/12.7.1 (Windows; Microsoft Windows 7 Ultimate Edition Service Pack 1 (Build 7601)) AppleWebKit/7604.3005.2001.1

we were ending up with a bunch of values like Windows 7 or Windows XP instead of just Windows like it's expected

This PR address this issue by:

• removing the regex that was causing this incorrect behaviour
• improving another regexp that was already addressing this issue, although partially
• adding more tests based on real user agents collected by our platform and fixing a couple of existing ones