Updates to dbuild 0.9.1, add sbt plugins

This pull request updates the community build to dbuild 0.9.1, and includes various Play components and other 2.10-based projects and sbt plugins.

These changes are provisional; cleanups and improvements are welcome. The list of 2.10 projects is not exhaustive: the "check-missing: false" option implies that a number of libraries that are dependencies are not currently included; more will follow over time.

Notably, the spaces setup for 2.10 projects is currently: ``space.from:[sbtplugins,sbtplugins]``, where the first refers to the main artifacts, and the second to sbt plugins. Therefore, the projects use the 2.10 artifacts both for their sbt plugins, as well as for their dependencies. That may easily lead to cycles: for instance, "sbt-site" uses itself as a plugin; therefore, some patience is needed while adding new dependencies. The cycles diagnostic in dbuild 0.9.1 has been further improved, incidentally. For some projects, a project-specific ``space:sbtplugins`` can be added, which means that the space is used to publish, and as a source of artifacts for the main build level, but not for the sbt plugins in use (see the spaces section, and the section on plugins in the manual for additional details).

This pull request is being validated by: https://jenkins-dbuild.typesafe.com:8499/job/Community-2.11.x-cunei/18/