Don't add generated folder to srcDirs

[mfulgo]

What I ultimately want is to add the generated files to version control so I can track differences in the files over time and customize the classes.

In an earlier version of the plugin, there was the option to output the generated files to a specified folder. That was removed, and now the generated files always go to build/generated/wsdl. The plugin now also adds that folder to the main Java source sets: https://github.com/nilsmagnus/wsdl2java/blob/master/src/main/groovy/no/nils/wsdl2java/Wsdl2JavaPlugin.groovy#L77

However, build directories are generally ephemeral and ignored by git. This means that I have to create a gradle task to copy over the generated files to something like src/main/java-generated and add that to my source sets. But, adding it to the source sets then causes problems because unless I remove the build/generated/wsdl directory, there are duplicated classes.

So, I can see three ways of resolving this:

1. Re-add the option to specify the output directory and keep the line that adds the output directory to the source sets. Or...
2. Don't add the output directory to source sets and require the plugin user to move the files around and add the desired director to the source sets on their own. Or...
3. Re-add the option to specify the output directory and get rid of the line that adds the output directory to the source sets.

Solutions 2 and 3 would also resolve issues #61 and #67.