Drop support for old skins that don't use head element

These skins have been obsolete since 1.16 and aren't supported well at this point.
This deprecates those skins and begins deprecation of the creation of <head> contents
with only chunks of OutputPage stuff. The entire head should be created by OutputPage.

This also deprecates some old methods responsible for returning raw chunks of html for the head:
* getScript
* getHeadItems

Output of HeadItems is also tweaked. Previously there was no newline added
after each item, now there is. Most of the callers of addHeadItem don't use
their own newline and as a result end up on one line.

Change-Id: I13e25cc8d8fc3aa682f23b019a2fda0e809a5f64