When selecting the time of metric's points only the time was selected,
not the date. The issue with this is mainly in the view "Last 12 hours".
Example:
It's 11:10 am and I choose the "Last 12 hours" view, the metrics points
will be from 23:00 yesterday to 11:00 am today.
When giving all these datas and labels to ChartJS, it sorts the points
by label from lower to highter. It means 23:00 (from yesterday) will be
after the datas of today, it doesn't have sense.
To fix it, I've added in the repositories the date in addition to the
time. So it's no longer 11:00 that is selected but 2018-01-15 11:00.
I've updated the Metric vue in order to cut the label when displaying so
it doesn't change the displaying.
Because there are metric views that are based on date but not time,
there is a condition in the Metric vue to cut the string only if the
time is present.
Related to CachetHQ/Cachet#2848
