Basic implementation of `bands.x`

[bastonero]

An implementation that wraps the binary bands.x was missing. This program is used to find the symmetries of wavefunctions, to re-order the bands, and to perform basic post-processings, such as the calculation of the momentum operator.

The current parser only performs basic parsing, with no specialized outputs for k-point wavefunction symmetries, nor momentum operator, nor bands. This can be, for instance, implemented over time depending on user request.

[bastonero]

Thanks a lot @sphuber for the review.

I was aware of the plugin, but thanks for the reminder, I wasn't aware of the very nice docs. Here I was interested to use the CalcJob/WorkChain for future composite WorkChains. But good to keep in mind about aiida-shell.

[bastonero]

PS: any idea why the docs is always failing lately?

EDIT: locally it builds w/o any warning

[mbercx]

PS: any idea why the docs is always failing lately?

Hmm, let me have a look 👀

[sphuber]

Fixed the RTD build so merging this. Thanks @bastonero