[ENH] Add pedigree reading handling for missing and member_index.

[IvoTod]

Is your feature request related to a problem? Please describe.
When fixing pedigree downloads in the federation, a difference was discovered between the downloads of remote and local study pedigrees, that went both ways. Local study pedigrees had tags and remote ones didn't. Remote study pedigrees had missing and member_index and local ones didn't. These are currently patched to work and require additional work in the pedigree loaders to load their types properly, as this was breaking all studies by making their family members appear missing, due to the value of missing being "False".

Describe the solution you'd like
We should be able to load pedigree files with missing and member_id columns.

Additional context
Related to this PR