Polish faces and fix many small bugs

* sly-autoloads.el (sly-contribs): Default this variable to a list
with `sly-fancy' as the sole argument.

* sly.el (sly-inspectable-value-face): Removed.
(define-sldb-faces): Removed unused faces
(sly-mode-line): Better face inheritance.
(sly--mode-line-format): Switch connection and package information.
(sly-message): Protect against message bodies with format
constructs.
(sly-minibuffer-respecting-message): Resurrect. Needed by
sly-fuzzy and sly-c-p-c contribs.
(sly-apropos-symbol): Better face.
(sly-apropos-insert-symbol): Better face.
(sly-xref-face): Removed.
(sly-xref): Use a proper `sly-part-button'
(sly-insert-xrefs): Pass more args to `make-text-button'
(sly-inspector-topline-face, sly-inspector-label-face)
(sly-inspector-action-face, sly-inspector-type-face): Removed.

* contrib/sly-c-p-c.el (sly-complete-symbol*): Don't call
`sly-maybe-complete-as-filename'. It has been removed.

* contrib/sly-fuzzy.el (sly-fuzzy): Insinuate into
`sly-complete-symbol-function' on load.

* contrib/sly-fuzzy.el (sly-fuzzy-insert): Don't error here, it's
annoying.

* contrib/sly-mrepl.el (sly-mrepl--insert-output): Use a face.
(sly-mrepl--insert-prompt): Include "> " in the propertized prompt.
(sly-mrepl-output-face): New face.
(sly-mrepl-prompt-face): Better face.

* contrib/sly-trace-dialog.el (sly-trace-dialog-part-button): Use a better
label.
(sly-trace-dialog--insert-trace): Use the normal face for
`sly-part' buttons.

* lib/sly-buttons.el (sly-action-face, sly-part-button-face): New faces.
(sly-action): Use `sly-action-face'