Fixes to WikiConfig: don't alias namespaces, magic words, etc.

By mutating {} and [] assigned to WikiConfig.prototype, all languages were
effectively sharing the same namespaceNames, namespaceIds, magicWords, etc.
Create these hashes and arrays in the constructor instead so they are
unique per-instance.

Change-Id: Idef86eae95c21d694ac02e519ed16b6596386350
Merge "Fixes to WikiConfig: don't alias namespaces, magic words, etc."