Energy graph overlaps with double strings

[jaspearias]

Test Device

Hanson

Operating System

Windows 10

Browser

Internet Explorer

Problem Description

For phetsims/qa#397
When testing double strings in the "Lab" screen the energy graph overlaps into the ground and the "Grid and Reference Height" check box.

Visuals

[jessegreenberg]

Thanks! Fixed in the above commit and the rest will be taken care of in #102