Display the currently assumed Wh/mile on the SOC/range graph

Tesla actually hides some capacity from the user, so displayed rated range
drops faster than SOC. This tooltip should make that visible.

Instead the tooltip shows that the current tooltip is picking up the wrong
values as the two arrays (SOC / range) come from different databases and
have different x value distribution. This needs a lot more work.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix the time offset issue in SOC/range chart tooltip

Since the two time series are independent, using dataIndex was a silly
idea. Instead it's much easier to use the datapoint[0] (i.e., the time
stamp of whatever point we're at) and then look up both values
accordingly.

If performance ever becomes an issue we should consider binary search here
:-)

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Merge pull request #34 from dirkhh/socRange

Soc range