container append loc default, linegraph "preprend" and some test work

* made the location argument of the SVGContainer.append method optional, defaulting to using the whole container.
* added an optional argument to LineGraph.append to allow appending "before" the graph data is drawn.
* did some work to the linegraph tests to allow adding them to the main test suite index.html, by using before and after methods to create the div and container and remove them as needed.