* It can be hidden by dragging it up/down.
* It can be at the top or bottom, independent of the header.
* It uses the color theme from the header.
* It does not change its color, when the area becomes active.
Currently, it is used in the text editor to display the file path.
Differential Revision: https://developer.blender.org/D4601
Also added keys for toggling harden normals,
and cycling through miter types.
Still to do: add some shortcuts for affecting the
spread value for arc miters.