graphie.fixedPath and graphie.fixedLine functions for wrapping lines and paths in DOM nodes

Summary:
Similar to graphie.fixedEllipse, these functions wrap Raphael objects in their own
DOM nodes that can then be transformed.

Test Plan: See [TODO].

Reviewers: aria

Reviewed By: aria

Differential Revision: http://phabricator.khanacademy.org/D14161