Cross-correlation studies

[Sebastian-Belkner]

It would be nice to have a study on cross-correlation to other lensing tracers, such as the CIB as this would add some great new features to delensalot:
Necessarily, we will have to add a suitable,

• likelihood model
• analysis

The core functions could be simply added, then the analysis recipe could be build by a cross-corr-configuration using an entry point that builds the right pipeline. This pipeline can be different to a standard re-analysis.