Arquillian - create JUnit's @Category appender

For tests which use the JUnit's @Category, this class needs to be added to the deployment.
It would be convenient to have this added automatically.

Aslak's note:

You can do this today if you want to, same as the weld core tests do.

Create a little AuxiliaryArchiveAppender that packages the categories. As long as that is registered in a LoadableExtension and register as SPI and on Classpath when you run, the produced Archive will be bundled with the deployment.

AuxiliaryArchiveAppender example:
https://github.com/weld/core/blob/master/tests-arquillian/src/test/java/org/jboss/weld/tests/CategoryArchiveAppender.java

LoadableExtension example: (only the service AuxiliaryArchiveAppender is needed in this case)
https://github.com/weld/core/blob/master/tests-arquillian/src/test/java/org/jboss/weld/tests/WeldCategoryExtension.java

SPI registration:
https://github.com/weld/core/blob/master/tests-arquillian/src/test/resources/META-INF/services/org.jboss.arquillian.core.spi.LoadableExtension