Replace *_STOCK with their non-deprecated counterparts

In gtk+-3.10 stock items have been deprecated:
https://docs.google.com/document/d/1KCVPoYQBqMbDP11tHPpjW6uaEHrvLUmcDPqKAppCY8o/pub

Replace the all the stock item references with their
suggested new counterparts.

Signed-off-by: Guido Günther <agx@sigxcpu.org>