Set Google Analytics siteSpeedSampleRate to 100

Google Analytics has some amazing site speed/performance monitoring features (the best i've seen). But by default the audience sampling size for such metrics is only 1%. 

This PR sets the sample rate to 100%. As I want to play and learn from these features :wink: 

More details here: https://support.google.com/analytics/answer/1205784?hl=en-GB