GTK2/3/4: Add return values to dw_window_set_bitmap(_from_data). Also similar to the other platforms, no longer install XPMs to gtk/. GTK4 is currently untested, if it doesn't work, may be a follow-up. Also fix a GCC fortify warning with strncpy().

[Desktop Entry]
Name=Dynamic Windows Test
Exec=@prefix@/bin/dwtest 
Terminal=false
MultipleArgs=false
Type=Application
Categories=Application;Development;X-Red-Hat-Base;