Allow docs jar to be configured via sbt setting
Move documentation test setup to docs sbt plugin
Make documentation jar optional
Add source url to published module descriptors
Package documentation in extra playdoc artifact
Remove twirl documentation
Add placeholder toc entry for play slick docs
Allow the omnidoc jar to be used

Added as a library dependency for non-snapshots by default.
Merge pull request #3598 from pvlugter/omnidoc

Aggregated documentation setup