PR #1139: Remove some of deprecated GTK stuff

PR #1139: Remove some of deprecated GTK stuff
https://github.com/BestImageViewer/geeqie/pull/1139

Remove deprecated gtk_adjustment_changed
Remove gtk_tree_view_set_rules_hint
Get rid of half of deprecated stock icons: menu items
Replace deprecated gdk_cursor_new with gdk_cursor_new_for_display
Add fullscreen icon
Replace deprecated gtk_tree_view_get_vadjustment with gtk_scrollable_…
Get rid of another big chunk of stock icons: buttons
Replace literal icon names with #defines in main.h, replace some icon…
Leftover cleanup after previous series of commits
Replace a few left literal icon names with #defines
Fix icons in sort bar and toolbar customization
Remove leftover line