Add clipboard feature

Use GTK to take the text from the clipboard.
Add `/paste` command which pastes this text now to console window.

src/command/cmd_defs.c

@@ -2415,6 +2415,19 @@ static struct cmd_t command_defs[] =
         CMD_NOARGS
         CMD_NOEXAMPLES
     },
+
+    { "/paste",
+        parse_args, 0, 0, NULL,
+        CMD_NOSUBFUNCS
+        CMD_MAINFUNC(cmd_paste)
+        CMD_NOTAGS
+        CMD_SYN(
+            "/paste")
+        CMD_DESC(
+            "Paste clipboard.")
+        CMD_NOARGS
+        CMD_NOEXAMPLES
+    },
 };
 
 static GHashTable *search_index;