Outliner navigation hotkeys

Simple hotkeys for Next, Previous, Child, Parent objects in the list.

Since Outliner at moment is getting some love with addition of collections I wanted to bump a feature that might be too small to bother as an individual project, yet gets handy when there is a lot of repetitive clicking work. Namely - Hierarchy navigation shortcuts: hotkeys for: next, previous, parent, child object (tree element).

The perfect hotkey would be main keyboard arrows. They are used as global animation scrubbing hotkeys, but since Outliner is unlikely to be used while scrubbing, those could be overridden locally. If that is objectionable, it would be great to have at least the function itself, so the hokey could be attached manually.

It would be ideal to some day have such navigation in viewport { may seem like a strange idea to iterate through object in effectively an "invisible list" just one by one, but it actually is very convenient and fast for things like character bones or other complex parenting structures that are conceptually simple, yet very hard to automate for easy selection in the viewport }, but the ability to do this in Outliner would be of great help already and a good improvement of navigation of Outliner (or even tree lists globally) as whole.