Changing default copyright notice per WMF Legal's suggestion.

Changing from "Content is available under $1." to...
"Content is available under $1 unless otherwise noted."

This is especially relavent to wikis that use InstantCommons.

Change-Id: I878372de6c42bcb7660b111911d0e12bb351d2c5
Merge "Changing default copyright notice per WMF Legal's suggestion."