ENH: Add new calculator file for VASP running interactively

As has been discussed a few times, this is the first public version of the VASP calculator running interactively via ASE. This provides quite a speed gain when running some methods and even allows things such as minima hopping to be used with VASP which previously was extremely slow. This calculator expects you to set up a VASP calculation and then allows you to use ASE's optimizers with it. Someday we can attempt to merge this into the main VASP calculator (letting us actually make the calculation as well, instead of just running it) possibly, but for now this is an important feature to be able to use with ASE.

A lot of internal testing has been done with this to make sure it runs well. Eventually some documentation should be written up on this (a test could be added to VASP's test too) but I think this should be added as is, as I won't have the time for a while to do this.

@ehermes should see this in particular, as we have discussed some details about implementation and he may have input.