Store bot status in attributes

[rmccue]

We currently store UA data in analytics, but don't separate out bot traffic. For example, the user agent for Googlebot is Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; Googlebot/2.1; +http://www.google.com/bot.html) Chrome/W.X.Y.Z‡ Safari/537.36 which will be identified as Chrome.

This means we later can't exclude bot traffic from reports.

Related: faisalman/ua-parser-js#227

[roborourke]

Bots are now excluded by default as they're not really useful for what we're doing with the data or useful to our customers without more advanced capabilities built on top.

#281 added the ability to not exclude bots as well, and in such cases we add attributes.isBot to the event data so we can query for its existence.