Consistent lensing for modified gravity

[damonge]

Being worked on with @noller The aim of this branch is to allow CCL to select the right P(k) when computing angular power spectra involving lensing in the context of non-LCDM theories, where psi != phi.

• [ ] Associate all tracers with a 3D cosmological quantity (e.g. delta_matter or delta_weyl)
• [ ] Allow angular_cls to select the right P(k) by default (unless provided).
• [ ] Get the Cosmology object to store at least the following power spectra: delta_matter:delta_matter, delta_matter:delta_weyl, delta_weyl:delta_weyl, both for linear and non-linear pks. In the first instance, forget about MG.
• [ ] Then, make sure any factors of Sigma are multiplied correctly.
• [ ] Extract these P(k)s from CAMB (and CLASS if possible)
• [ ] Same for isitgr.
• [ ] Document what delta_weyl means.
• [ ] If the non-linear Pks are not provided, then we halofit them.
• [ ] Add a warning when the above happens (since this is wrong at some level)

Once the above is done, we need to worry about:

• [ ] Remnant growth factors in IAs and RSD
• [ ] Decide between the delta_weyl and phi_weyl nomenclature.

[coveralls]

Pull Request Test Coverage Report for Build 3931842083

• 3 of 3 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 97.529%

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Totals
Change from base Build 3862532670:	0.001%
Covered Lines:	4855
Relevant Lines:	4978

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💛 - Coveralls