Make wiki pages global

[GoogleCodeExporter]

Currently, wiki pages are associated with collections and can only query data 
in that collection.  

This enhancement would make the "wiki page" component of the system a 
server-level object rather than having several Wiki objects, one per 
collection.  It would also allow writing queries that access data from more 
than one collection (which might in turn require some modifications to the 
schema language to provide top-level variable bindings for the different 
collections).

This would also mean that we could write documentation for the whole system as 
(global) wiki pages, making it more self-documenting.

Original issue reported on code.google.com by [email protected] on 12 Feb 2015 at 4:09