Add user checkboxes for graph selection

[rosshamish]

• allow user to select x and y axes
• use http://tutorialzine.com/2011/03/better-check-boxes-jquery-css/

[rosshamish]

they've been added, now they just need to be made functional

[rosshamish]

Functional. Closed with commit 27557306bdd06d1150b3531469344a5070e3f95a