4.15.1

- Switch XfceTitledDialog to headerbar layout
- XfceTitledDialog: Keep buttons in the action area
- XfceTitledDialog: Also repack xfce_titled_dialog_new
- XfceTitledDialog: Make sure windows can be dragged
- XfceTitledDialog: Add _create_action_area, _add_button
  and _add_action_widget
- Introduce xfce_titled_dialog_set_default_response
- Mark xfce_titled_dialog_new_with_buttons as deprecated
- Add two new functions to search for app icons
- xfce-about: Fix Makefile
- shortcut-dialog: Show dialog content (Bug #16338)
- xfce-dialogs: Use GtkMessageDialog as base class
- xfce-dialogs: Improve layout of confirm_close_tabs
- xfce-dialogs: Improve alignment and layout of dialogs
- xfce-dialogs: Add right margin back to labels
- xfce-dialogs: Drop default window titles
- docs: Add xfce_dialog_confirm_close_tabs
- tests: Add xfce_dialog_confirm_close_tabs
- tests: Improve UI
- tests: Add icons to dialog buttons
- tests: Simplify code by using XfceTitledDialog
- tests: Re-order buttons
- tests: Fix typo in test-ui.c (Bug #16253)
- Rename test-ui-gtk3 to test-ui
- Improve docstrings
- Fix typos
- Drop gladeui Gtk2 from distcheck options
- Drop unused declaration
- Fix compiler warnings
- Remove trailing whitespace
- Always provides needed files for vala binding in dist tarball
- Add recents functions to libxfce4ui.symbols
- Drop xfce-header from pot files
- Update docstrings
- Fix license text box too small (Bug #16259)
- .gitignore: ignore all .o files
- Make autogen output friendlier
- Translation Updates:
  Albanian, Bulgarian, Catalan, Chinese (China), Croatian, Danish, Dutch,
  French, Galician, German, Hungarian, Italian, Japanese, Lithuanian,
  Norwegian Bokmål, Polish, Portuguese, Portuguese (Brazil), Russian,
  Serbian, Slovak, Slovenian, Spanish, Swedish, Turkish, Ukrainian