Fix #63: Use auto-value for Event classes.

@hamidp I'm stealing this from you ;-o

OK, it comes from this guy
https://github.com/nebula-plugins/gradle-extra-configurations-plugin/blob/gradle-1.12/src/main/groovy/nebula/plugin/extraconfigurations/ProvidedBasePlugin.groovy

And it does what we don't want - Making `compile` depending on `provided` :-(

I think the workaround in this change is reasonable at this point, but probably we should talk to
nebula-plugin's team.