Blender Git Loki

Property Search: Move properties context buttons back to a panel

The context path buttons used to be in a panel in 2.79. Although they look
a bit better in the header, there is not space for them with the property
search field in the header as well.

In the long term, maybe it will be possible to shrink the text button and
then animate it expanding when property search begins, then there
would be enough room for both.

Note that this diff is just for review, Blender won't ever actually have only
the pin button in the header like the following image.

{F8858554 size=full}

Differential Revision: https://developer.blender.org/D8853