SI-7201 scala-library's pom points to scaladoc url

The project/properties/info.apiURL pom property is used by SBT
to link to an artifact's scaladoc.

For scala-library version $v, the url is http://www.scala-lang.org/api/$v/

I verified the substitution works by inspecting the pom generated by `ant deploy.local`

review by @harrah or @jsuereth