Update example plugin
I noticed that the example plugin does not compile anymore (I noticed because my custom plugin, based on the example plugin, didn't compile anymore :P). Maybe it's possible to add this plugin to CMake, then you know immediately if something is up. (Is that possible without having it shown in the GUI? On the other hand... since it's in Misc. you can maybe use it to point out that people can create custom plugins, like an advertisement plugin)