Service Catalog tree fixed to not show Actions nodes below Service nodes

Moved x_get_tree_st_kids method from parent TreeBuilderCatalogsClass to subclasses TreeBuilderCatalogItems and TreeBuilderServiceCatalog, so each can determine what to draw in the tree.

Screenshot of Actions tree node that shouldn't be there:
![screen shot 2014-07-08 at 1 22 41 pm](https://cloud.githubusercontent.com/assets/3433754/3516176/b47f521e-06dd-11e4-82e6-850fff409054.png)

@h-kataria please test