We now select the LayerCollection at index 0 for the active ViewLayer after a collection deletion operation. Added some functions to query outliner tree data & get LayerCollection by index using a similar approach as we do for SceneCollection indexing. With warning and style cleanups by Dalai Felinto. Reviewers: dfelinto Tags: #bf_blender_2.8 Differential Revision: https://developer.blender.org/D2942