Implemente layer box

* Layers can be added dynamically
* Layers are sorted

TODO:
- implement load and save functions

layer-selector.h

@@ -0,0 +1,23 @@
+#ifndef __LAYER_SELECTOR_H__
+#define __LAYER_SELECTOR_H__
+
+#include <gtk/gtk.h>
+#include <glib.h>
+#include "layer-element.h" 
+
+struct layer_info {
+    int id;
+    /* This contains both: opacity and Color */
+    GdkRGBA color;
+};
+
+void generate_layer_widgets(GtkListBox *listbox, GList *libs);
+void clear_list_box_widgets();
+
+void setup_load_mapping_callback(GtkWidget *button);
+void setup_save_mapping_callback(GtkWidget *button);
+
+void get_layer_info(GList **info_list, GtkListBox *box);
+
+
+#endif /* __LAYER_SELECTOR_H__ */