start fixing screen_ctx usage, for it is utterly broken. bring font

into screen_ctx and start passing screen_ctx around to in order get rid
of Curscreen; fixup per-screen config colors the same way.

diff mostly from oga@, with a bit harsher reaction to the state of screen_ctx.

"please commit" oga@

calmwm.c

@@ -156,10 +156,10 @@ x_setupscreen(struct screen_ctx *sc, u_int which)
 	sc->xmax = DisplayWidth(X_Dpy, sc->which);
 	sc->ymax = DisplayHeight(X_Dpy, sc->which);
 
-	conf_color(&Conf);
+	conf_color(&Conf, sc);
 
 	font_init(sc);
-	conf_font(&Conf);
+	conf_font(&Conf, sc);
 
 	TAILQ_INIT(&sc->mruq);