Legend items show with dashed lines of the appropriate stroke-dasharray

This makes the most sense for a composite chart with several line charts that have different dash styles.

If any of the legend items have a stroke-dasharray property, all the legend items will show as lines.

Added an example with a composite chart that has different dash styles for each line graph.
Merge pull request #393
Use queue for composite example, lint
Added legend with colors for pie chart
added hover highlighting via legend
refactored out repeated code in legend stuff
refactored stack hiding out of legend and into stackable charts
Added filtering for pie chart through legend
Finished refactoring knowledge of stackable charts from legend. Charts now can tell whether a legendable is hidden
Merged pie chart legend changes.