Merge in files from Build a Nucleus

[chrisklus]

In order to add a build-a-nucleus sim owned by PhET (that uses build-an-atom code from master), we need to have @Luisav1's copy of shred merged with phet's shred

[Luisav1]

Changes to do on Build a Nucleus files

ParticleCountDisplay

• only removed electrons, and particle count display. Can be handled w an option.

ParticleNode

• added Z layer property, can be handled in option

AtomNode - NucleusNode

• could be created as a new file or subclass

ParticleAtom - ParticleNucleus

• make a seperate file for this

New files

• NucleonShellView.js - check w ElectronShellView duplicated code
• NuclideChartCell.js - check w PeriodicTableCell duplicated code
• NuclideChartNode.js - check w PeriodicTableNode duplicated code
• NuclideChartX.js - check w PeriodicTableCell duplicated code
• ParticleAtomDisplay - check with duplicated code on ParticleCountDisplay

[pixelzoom]

@chrisklus This appears to be causing lint-everything failures in CT, reported for repos shred and perennial.

[chrisklus]

The initial commits were done on master, then moved to the branch buildANucleus (which is now buildANucleusDeprecated). Closing.