Add legend to graph

[lorddev]

For users with multiple pages of archived habits, correlating the colors of checked habits with the colors on the graph may be difficult to do without printing out the page, as the graph and the habits may not appear on the same screen. Two solutions would help with this problem:

1. Add a legend to the graph.
2. Use framing or div scrolling to allow the graph to stay in view when scrolling through the habit list.