Add dependency="true" in feature generation

From Robert's email to odlparent-dev:

Because we never ever want to reinstall a feature. Once a project's
feature is installed, it is activated and therefore should not be
further disturbed. This is especially true for bundles which include
models, as their movement triggers SchemaContext recomputes.

I am not sure this flag has an effect, but it looks that way – there is
not much in terms of documentation.