Simplify and fix the partition reader
Simplify and fix the partition reader

This fixes the partition reader to correctly set the upper bound of the
partition ids. Furthermore the partition reader is simplified to create
the partition directly in the partition instance instead of a separate
vector as the partition instance also simply expands a std::vector when
new nodes are added.

fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit,fmaschler/networkit