Parsing and pass velocities in CONTCAR

[zhubonan]

What should happen

For MD simulations one wants to restart the calculation using the same structure as well as the velocities. However, we don't parse the structral part from the CONTCAR as the moment, and VaspCalculation does not have velocity inputs.

What happened instead

Allow simple restart from CONTCAR for MD simulations. The volecities should be parsed and stored either in StructureData or and ArrayData node, and can be paseed to VaspCalculation for restarts.

Related to: aiida-vasp/parsevasp#117

[sylviancadars]

Hi,
And I wish to add that this also raises the separate and yet related issue of retrieving and concatenating trajectories as well, as pointed out in a related issue in aiida user's group).
Best wishes.
Sylvian.

[atztogo]

The trajectory may be better to be supported as being retrieved from the hdf5 file. Otherwise the (text) file can be too large to transfer.