This commit removes the propdeps plugin.
"provided" configurations are replaced with "compileOnly", "testCompile"
configurations.
The "optional" configuration supported by propdeps is now replaced by a
local Gradle plugin defining a specific configuration for that.
As a result of that change, optional/provided dependencies are not
published with the POMs anymore.
This commit introduces the Spring dependency management Gradle
plugin. All dependency versions and BOMs are now managed in the
root project and declared in the modules directly.
