Bugfix: make server buildable again

The server was not buildable because the processor-plugin did run before the ANTLR-Plugin did its job and created the classes from the grammar. This is fixed by this pull request. 
not finding the antlr generated classes should not result in a build failure, at least it does not on my machine. but if this change gets rid of the misleading error message during the maven build then i am totally fine with it.