Allow to set-up MapStruct for Java projects through the plug-in

Nadie ha tomado este issue todavía.

When working with a Maven project for which MapStruct is enabled (e.g. through via maven-processor-plugin), upon import of the project M2E will automatically configure the Eclipse project to run the MapStruct annotation processor.

But for plain "Java Project"s it'd be nice if the plug-in could be used to set up MapStruct. It could like this:
- Under "Project Properties" have an entry "MapStruct"
- On that page have a check box "Enable MapStruct for this project"; When checked this should register the annotation processor (AFAIK there is an extension point through which APs can be registered)
- Allow to specify the processor options through check boxes as well
- Optionally, have a global preferences pane which can be used to configure default values for the processor options which would be overridden by project-scoped settings

@larswetzer WDYT, would that make sense?

Comienza revisando el punto de extensión de Eclipse para el registro de annotation processors y cómo se proporcionan las propiedades del proyecto y las preferencias globales para proyectos Java simples. Se considera terminado cuando el plug-in puede habilitar MapStruct, configurar las opciones del procesador en el ámbito del proyecto y proporcionar opcionalmente valores predeterminados que las configuraciones del proyecto puedan sobrescribir.

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