Blender Git Loki

Outliner: Allow select on row icons

Allow selection of subtree elements on a collapsed element's
row. Because subtree elements are aggregated by type, a select on
an icon that represents multiple subtree elements will invoke a
popup menu to select the specific subtree element.

Also draws highlights on cursor hover over a row icon.

Any child elements that are linked to multiple collections will
only be listed in the popup one time, and selection from the
popup will select the first instance in the subtree.