Package Maven Plugin: Add "accessControlHandling" property

currently, it is only possible indirectly via the "properties" property to set the "acHandling" package parameter. furthermore it is not mentioned at all in the plugin docs, nor its possible values.

as the "acHandling" package property is used quite often in package definitions it would be useful to have a property in the mojo itself, same as it is the case for "requiresRoot", "allowIndexDefinitions", "packageType".