resourceloader: Move logo preload from OutputPage to SkinModule

resourceloader: Move logo preload from OutputPage to SkinModule

This was introduced in OutputPage before support for getPreloadLinks()
was added to ResourceLoader. The introduction in ResourceLoader was
actually inspired by this original implementation.

Now that we have it, we should make use of it for this module
as well. Doing so has several benefits:

* Makes the code cleaner by not requiring every skin to implement
  the extra boolean method. Instead, it naturally works. If
  the skin loads the SkinModule, it gets the preload as well.
  If not (such as Minerva, which has a different logo config),
  then it also doesn't get the preload link.
  Naturally, automatic.

* Makes code cleaner by not having static methods, and by not
  having OutputPage call into a Module class.

* Fixes the problem where, if a site's logo is changed, all cached
  HTML is preloading the old logo whilst the stylesheet fetches
  the newer one. Causing both to be downloaded.

* Still preloads the logo well before it can render.

Change-Id: I11b390f2e4f5e7db8b4506ab547839152888005c