Added support for queries against Materials Project

[espenfl]

Need to be able to pull data from the Materials Project. In this prototype, only the extraction of the structure is included. However, this can obviously be extended.

[coveralls]

Coverage increased (+7.6%) to 68.572% when pulling 2a38624 on espenfl:mp_import_support into 348665e on aiidateam:develop.

[merkys]

Please address the in-line comments on the code. The rest of the code looks OK. It would be great if you could supply a couple of tests for the parts of the code that do not need the network access.

[espenfl]

Yes, in fact I also wanted some tests for the actual pull, but then we need the key. A public test key supplied by MP would be great (e.g. just pull one demo structure for instance) but I do not know of such functionality at the moment. Right now I think the only sensible test is to test that an invalid key returns the right error message or something similar as that is already in __init__. I will add such a test for good measure.

[merkys]

Yes, in fact I also wanted some tests for the actual pull, but then we need the key. A public test key supplied by MP would be great (e.g. just pull one demo structure for instance) but I do not know of such functionality at the moment. Right now I think the only sensible test is to test that an invalid key returns the right error message or something similar as that is already in __init__. I will add such a test for good measure.

I guess we're OK with tests that do not interact with the API for now. We might test the generation of Results and Entry instances.

[merkys]

One more note on plugin naming: I suggest using full names (matp.py -> materialsproject.py, MatProj* -> MaterialsProject*) as neither matp nor matproj seem to be upstream-preferred abbreviations of the database. I admit that shorter names are faster to type, but they might be non-trivial for new users. There is actually a nice Wikipedia guidelines article on abbreviating things that is good to refer to, IMHO.

[espenfl]

Yes, but I just followed what was there already. Totally agree on this topic. I also believe this should be done in the code, regardless of clutter and longer lines. Changed this now, but will leave the old stuff for now.

[merkys]

The importer seems to have disappeared from this PR... Could be due to rename?

[espenfl]

Should be fine now. Also added the aiida.tools.dbimporters.plugins to the test folder as that was not there.

[merkys]

Great! It's very close to be finished. I have noted a few minor changes, and then we are ready to merge.

[merkys]

Good to go. Many thanks!