Add "clear()" to Associative interface

src/lib/Interfaces/Associative.vala

@@ -6,6 +6,7 @@ namespace Invercargill {
         public abstract void @set(TKey key, TValue value);
         public abstract bool add(TKey key, TValue value);
         public abstract bool remove(TKey key, out TValue? value);
+        public abstract void clear();
 
     }