(bug 38559) Add hook to info action to allow extensions to add extra

(bug 38559) Add hook to info action to allow extensions to add extra
information to a pages info

* Added new function, pageInfo, to return page information in easily
  manipulated format.
* Added call to wfRunHooks.
* Moved credits to follow the footer (this is a change for my
  aesthetics that may be reverted, but it also allows admins to more
  easily add a horizontal break or some such in pageinfo-footer).
* All messages are escaped.

Have tested extensively, all information is rendered exactly as it
was before as far as I can see.

Change-Id: I702f2f13d3b7af26d89c4fd9002d3161dc7905d2