Add filtering to SceneHierarchy editor

[bentoogood]

Users should be able to filter the displayed contents of the SceneHierarchy editor by

• type ('show just cameras')
• name ('show droidArm')
• other?

[andrewkaufman]

The filtering could be based on custom columns suggested in #820. Is it actual filtering, or just sorting or colour coding.

[johnhaddon]

I think it's actual filtering being requested, as in items will be hidden. In the case of the name filtering it should be similar to the wildcard filtering in the file browser I think…I think that was Ben's initial intention anyway...

[bentoogood]

Filtering makes more sense to me, given the aim to handle scenes with 100000s of items.
Scrubbing through a list to find the highlighted items might negate the benefits...