(bug 31068) Set up NS_PROJECT for azwikibooks

This is a follow-up to I7e4b069; the namespace
name has to be defined with $wgMetaNamespace
because we use a default for all Wikibooks wikis;
I didn't notice that because someone cannily hid
it between individual wikis instead of placing it
at the top of the section (this is now fixed).

Bug: 31068
Change-Id: Ic9fbc8baf791badd3688dd272ae65d0183691d53