Basics: realMoleculeShapesProperty includes values that are only valid in the full version

[arouinfar]

Related to #223

The valid values of realMoleculeShapesProperty seems to be the full list of molecules available in Molecule Shapes. If you pass in a value that only appears in Molecule Shapes, Studio will not stop you.

For example, set the value to SF4 and it will appear to work, but the sim encounters a fatal error and freezes.

@jonathanolson should the validation be limited to the 5 molecules in Molecule Shapes: Basics?

[arouinfar]

Tagging for phetsims/qa#845.

[zepumph]

I was able to get this done by having the Property get validValues to start with. @arouinfar how does that look?

[arouinfar]

Thanks @zepumph! Everything looks good in master.