removeParticle from BANScreenView can be move to BANModel and renamed

[Luisav1]

From #112. removeParticle in BANScreenView only removes the particle from the model particle arrays so it can be move to BANModel.

BANModel already has a removeParticle function that removes particle's from the particles array. So a rename and maybe an investigation into why there are so many removeParticle functions would be good to do.

[zepumph]

@Luisav1 and I simplified the removeParticle() logic so now there is just a function on the model, and ParticleAtom (plus some overrides). We like this better than having things in the screen view. Closing