v6. Add command for reviewing and editing managed faces. Rework
properties applied to face symbols.

Previously, tuning this module's options to arrive at a satisfactory
palette was a bit inconvenient because you had to scroll around in
different target buffers afterward to get a sense of the result, which
was often only subtly different from a previous incarnation. Editing
persistent faces was also somewhat unpleasant for similar reasons. This
adds a single dashboard based on `list-faces-display' for doing both.