Upgrade to Groovy 2.3.0

Upgrade Boot to use Groovy 2.3.0 and provide dependency management
for all of Groovy's modules.

Closes #647
Remove duplicate hibernate-validator dependency from pom
EmbeddedDatabaseConfiguration -> EmbeddedDataSourceConfiguration in docs

fixes #791
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  EmbeddedDatabaseConfiguration -> EmbeddedDataSourceConfiguration in docs
  Remove duplicate hibernate-validator dependency from pom
  Upgrade to Groovy 2.3.0
Registering PID file to be deleted on JVM exit