Added spring-cloud-starter-archaius so downstream projects
like consul and zookeeper don't need to maintain the list of
archaius depenencies.
fixes gh-765
The new module is a BOM that doesn't have any parent or direct
dependency management in spring-boot-*. So users can include it
in their dependency management without polluting the spring boot
dependency versions.
Luckily it can also be used in the main spring-cloud-netflix pom,
which should no longer be used as a BOM.
