Enable plugin configuration in settings.xml

Currently there is no way to correctly persist user-specific configuration of plugins.
There are many plugins, that do not affect the build process, and should therefore NOT be configured in pom.xml (and versioned and released etc).

This is most annoying with IDE integration plugins. In a team, some developers use IDEA, some Eclipse, some Netbeans or anything else. It is apparently a nonsense to preconfigure anything about IDEA in pom.xml and commit it to the repository, because others either do not care or perhaps want different settings.

Ideally, it should be part of profile section. And to make the things really correct, each plugin (or even parameter?) should specify whether it can be configured in pom only, in settings only, or in both; one of these options might be used as the default.

This feature will greatly improve the pom's reputation of being a project descriptor, instead of being one user's setup.