Tweaks for skins:

Tweaks for skins:
* Moved SkinTemplate::addStyle() and related stuff to OutputPage so that it can be used non-SkinTemplate skins and avoid duplication with the actual OutputPage::addStyle() (the two functions have the same format).
* Non-SkinTemplate skins now also load their CSS with <link> tags instead of @import.
* Moved SkinTemplate::setupUserCss() to Skin.
* Merged action=raw&gen=(js|css) for SkinTemplate and non-SkinTemplate skins, renamed functions to Skin::generateUserJs() and Skin::generateUserStyleSheet() and dropped a lot of cascading call which is a bit incomprehensible.