Add iterative templates. (#1046)

* Store the "iterator" property on an individual template.

* Deal with the iterator key in the gen templates.

* Add iterator over all available clusters.

* Clean up the code a bit.

* Add selectedCluster iterator and clean up the code a bit.

* Add selectedCluster iterator.

* Add more iterators.

* Add pattern replacement for filenames for iterator files.

* Clean up the "side" issue.