add unit options
better time formatting
add weeks to time formatting
fix units
display date in tooltips
fix range chart
fix/improve time normalization

- until now, accessed_at-minutes were ignored
- now, “hours_since_release” is exact to the second
- for performance reasons, hours_since_release is precalculated and
stored in DIC table
add weekdayChart
enhance
weekdayChart: shorten x-axis labels