Merge ASE-based espresso parser from medford-group

[maxhutch]

All I've done so far is branch of medford-group/espresso and merge in CitrineInformatics/develop, resolving the conflicts. This probably won't work yet, but opening the PR will get travis tests going.

CC: @ajmedford

[ajmedford]

Thanks Max! We didn't quite get this buttoned up last time we worked on it, but plan to put some more effort in before the end of summer. Having the CI tests will help give us something to shoot for. I believe our GPAW parser is also in this branch, so it may need to be renamed in the future. We can cross that bridge when we get there.

[maxhutch]

@ajmedford I have some cycles to put into the QE parser this week and the next. I was going to just pick out your ase-based parser and either combine it with the existing parser or replace it outright. If you'd like, we could sync up on what your opens are try to get your group supported from the main branch again.

wrt GPAW: it looks like there is some stuff in the examples, but no parser

[ajmedford]

@maxhutch Sounds good - It looks like the GPAW parser is actually in another (student) repo so we can merge that in later.

I think having an ase-espresso parser is a good idea, but I think it might be a good idea to separate the "ASE" part and the espresso-specific parts. The former is probably much more impactful, especially since you already have a PWscf parser. It might be worth looking at Kitchin's ASE-mongo implementation too. Having a way to easily put an ASE atoms object (and its associated calculator parameters) into a .pif file would be very helpful.