add "getCollectionLink" convenience method to page object

If I have to type out `Loader::helper('navigation')->getLinkToCollection($page)` one more time, so help me god. ::shakes fist in anger::

(I kid, I kid... but seriously, this should have been done in 2007).
pass thru misc getLinkToCollection args
Merge pull request #1639 from jordanlev/patch-5

add "getCollectionLink" convenience method to page object