Update "install_requires" from aiida to aiida-core

[chrisjsewell]

One of the major reasons to do this is that readthedocs builds seem to fail with aiida (https://readthedocs.org/projects/aiida-crystal17/builds/7693840/) but not with aiida-core

I'd also note that, for some reason I get an ImportError for pgtest during tests, unless I specifically but it in the requirements (even though it seems to be in the aiida-core[testing] requirements?)

{
    "install_requires": [
        "aiida-core>=0.12.0,<1.0.0"
    ],
    "extras_require": {
        "testing": [
            "aiida-core[testing]",
            "wheel>=0.31",
            "pgtest"
        ]
   }
}

[ltalirz]

Thanks a lot for these suggestions, will look into this!

[ltalirz]

I can reproduce the pgtest import error

The travis log shows that pgtest is not installed (nor are any other "testing" dependencies of aiida-core).
This is not the fault of the aiida-core wheel used, whose METADATA contains the line

Requires-Dist: pgtest (==1.1.0); extra == 'testing'

It turns out that putting the same dependency with different extras is an unresolved pip issue.
It means we will need to replicate the dependencies needed for testing.