Implement shell prediction without charge groups
Prediction of shell positions reduces the number of iterations and makes generating initial coordinates easier. But prediction requires the coordinates of atoms involved in the local shell interactions. With charge groups these atoms were mostly within the same charge group. But with the Verlet scheme there are no charge groups.
1) Implement additional communication for these atoms, can be done analogously to vsites.
2) Predict based on shell displacements/velocities. Currently velocities are zeroed. It's somewhat tricky to keep track of displacements and this solution will not help with generating initial shell coordinates.