Include timestamp into NavigationInfo

[whimboo]

For page load analysis and HAR file generation the individual navigation events have to include a timestamp, which is not the case right now.

[whimboo]

For some more details see #204 (comment).

Hereby the Navigation Timing interface seems to be relevant. I assume those entries should be used instead of internal timestamps when relevant events like DOMContentLoaded and load are received?

[jgraham]

#346