Human readable debug

Leverage the code that writes a preset to XML so that messages
can be displayed in a human readable format.

E.g.,

(6, 2432, 1280)  Distortion: Dist Type: Screamer

The 3-tuple is position, id, value, which is followed by the
colon separated decode of the position, id, and the mapped value.

effects.h

@@ -116,6 +116,7 @@ typedef struct {
     gint n_banks;
 } Device;
 
+gchar *get_position(guint position);
 ModifierGroup *modifier_linkable_list();
 void modifier_group_free(ModifierGroup *modifier_group);
 void get_values_info(EffectValues *values,