Fix positioning of last candlestick and info popup showing incorrect info

It appears that the last candlestick is positioned off of the right hand side of the graph.  It also appears that the info popup shows the info for the wrong candlestick.  For example, when you hover on the first candlestick, the popup actually shows data from the second element of the data source.

To address this, this pull request adds a period option which should be set to the number of seconds that each candlestick represents.  It also ensures that the bisectDate function returns the correct index so that the info popup shows data for the correct candlestick.