rewtguy/pidgin

Replace gtk_image_new_from_stock with gtk_image_new_from_icon_name

I grepped through the code and no one is passing anything other than NULL, but
the function was still calling the deprecated function.

Testing Done:
Ran the unit tests and verified the menus in the blist and convwindow were still working.

Reviewed at https://reviews.imfreedom.org/r/1001/
if ENABLE_DOC
subdir('reference')
endif
if ENABLE_GTK
pidgin_man = configure_file(
input : 'pidgin3.1.in',
output : 'pidgin3.1',
configuration : man_conf,
install : true,
install_dir : get_option('mandir') / 'man1')
endif
if enable_consoleui
finch_man = configure_file(
input : 'finch3.1.in',
output : 'finch3.1',
configuration : man_conf,
install : true,
install_dir : get_option('mandir') / 'man1')
endif