Loading Google client services is a little monster, eating around
2MB (opcache enabled) of memory. As far as we instantiate the
repository instances really early, no matter they are not used
later (editor, file picker, admin...).. we are delaying the
load of the service until we know we are going to use it.

Surely applying this very same (sort of lazy load) techinque
to other repositories could lead to a nice memory reduction
in lots of pages.

MDL-50176 repository_youtube: also delay the inclusion of client.

While memory was fixed with previous commit, still some extra included
files where being reported, so go crazy and move all the stuff to
the new init delayed method.