Update lab-grapher submodule
_grapher.sass ➙ _bar_graph.sass :  it defines bar graph styles only

bar-graphs are defined in the lab project, and have no lab-graph reps.
The SASS should be named accordingly.

[#61295834]
https://www.pivotaltracker.com/story/show/61295834
Use Sass CSS Importer Plugin to combine lab-grapher css file into lab.css

Here’s the link to the sass plugin: http://bit.ly/1fqXQk1

[#61295834]
https://www.pivotaltracker.com/story/show/61295834
Remove sass-importer plugin, its a bit raw.

[#61295834]
https://www.pivotaltracker.com/story/show/61295834
grapher.build.js, lab.build.js &etc.: + Require paths lab-grapher.

[#61295834]
https://www.pivotaltracker.com/story/show/61295834
public-api.js : export Lab.grapher.Graph

[#61295834]
https://www.pivotaltracker.com/story/show/61295834