Support strings in namespace weights

This is much more convenient when specifying configuration across many wikis
that do not share consistent namespace numbering but do consistently alias
namespaces.  For example: most wikisources alias the 'Author' namespace
to the word 'Author' in their language but that namespace is sometimes 100,
sometimes 102, somtimes 104, and sometimes 106.

Bug: 69771
Change-Id: Ice3febecd8cd39c551d2809f1a88a6c8c91fae26
Merge "Support strings in namespace weights"