Invalidate cached pixmaps on reload and redraw.

After a reload, the drawing parameters for the decorations might
have changed, so we need to invalidate the cache and force a redraw
of the currently visible decorations. Also, don't leak the previous
font when reloading by freeing it before parsing the config.

include/data.h

@@ -119,7 +119,6 @@ struct deco_render_params {
     Rect con_deco_rect;
     uint32_t background;
     bool con_is_leaf;
-    xcb_font_t font;
 };
 
 /**