Revised handling of GIF animations

- New option `-a`: Play animations at startup
- Ctrl-Space toggles animation for all GIF files
- Infinite loop for all animations

config.def.h

@@ -34,13 +34,6 @@ static const float zoom_levels[] = {
 /* default slideshow delay (in sec, overwritten via -S option): */
 enum { SLIDESHOW_DELAY = 5 };
 
-/* default settings for multi-frame gif images: */
-enum {
-	GIF_DELAY    = 100, /* delay time (in ms) */
-	GIF_AUTOPLAY = 1,   /* autoplay when loaded [0/1] */
-	GIF_LOOP     = 0    /* loop? [0: no, 1: endless, -1: as specified in file] */
-};
-
 /* gamma correction: the user-visible ranges [-GAMMA_RANGE, 0] and
  * (0, GAMMA_RANGE] are mapped to the ranges [0, 1], and (1, GAMMA_MAX].
  * */