Mahendra Mariadassou

Add microcosm data to PLNmodels

1

Add data from the MICROCOSM study to the PLN package

Allow for null (or infinite in log-scale) offset in various PLN methods by using a "mask" to sum only over other variables when computing the ELBO of the model.

Add tests for graphical output

1

Use [vdiffr](https://github.com/r-lib/vdiffr) to add tests for graphical output. Seems to work nicely with base graphics and ggplot but less so with grobs.

Change `compute_offset` so that it can compute "block-wise" offsets (for example one for bacterial taxa and one for fungal taxa).