Also, add type hints for some of the field.alias properties
because mypy was getting confused.

This is needed for the field_set calculations

A common field that all nfpm packages will share,
making it easier to build a common FieldSet base.

Almost all fields are "required" in that, if present, they are
used in the generation of the package.

Users do not have to supply them, but the fields have to exist
on the Nfpm*Package targets.

This reverts commit d41a201.