Integrated nuclear fits

[Radonirinaunimi]

A re-implementation of the integrated nuclear-PDF fits based on the refactors.

Remaining to do:

• Improve and re-organize the writer and vpinterface modules
• Accommodate the computation of integrability and arc-lengths to properly account for $A \neq 1$
• Properly write the predictions onto disk and modify the way evolution is applied accordingly
• Fix broken tests
• Extend the report to include nuclear predictions

Checks:

• Standard fits in which only proton-like data are included (report)
• ...