This commit applies the Dependency Management Plugin to modules that
require it; right now Spring Framework is importing BOMs for Netty and
Reactor dependencies only.
Instead of applying those BOMs to all modules, they're applied only
where they're needed.
Issue: SPR-15885
The main `build.gradle` file contains now only the common build
infrastructure; all module-specific build configurations have
been moved to their own build file.
Issue: SPR-15885
Juergen Hoeller
Brian Clozel
Sebastien Deleuze