[31] Left Nav 

Updates to left nav...trying to reconcile the design (which looks to be re-purposed from [Sandstone Guidelines Site](http://www.mozilla.org/en-US/styleguide/websites/sandstone/) and our Information Architecture.

We cannot have the exact same UX, as the guidelines site uses left nav with trees that have intermediate nodes you cannot click to, they only server to organize the hierarchy of child nodes.  Our site has click-through intermediate nodes.

So...no granular slideup/down on click, as we must be able to actually click through and reach each node in the tree.