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

还没有人认领这个 Issue。

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?

首先检查 Eclipse 的 annotation-processor 注册扩展点，以及如何为普通 Java 项目提供项目属性和全局首选项。完成的标准是：该插件能够启用 MapStruct，在项目范围内配置处理器选项，并可选择提供默认值，且项目设置能够覆盖这些默认值。

由索引模型根据 Issue 内容生成。