feat: convert bookmarks to tags with color highlighting

- Add COL_COLOR column to bookmark tree store (bookmarks_treeview.h/c)
- Add color attribute to XML folder nodes (xml.c/h)
- New folder dialog with color picker (ui/folder.gtkbuilder, ui/folder.glade)
- Tag color saved and restored from bookmarks.xml
- Verse highlighting in Bible text using tag color (display.cc)
- Text color auto-adjusted for dark backgrounds (luminance)
- Multi-reference support: semicolons, commas, verse ranges
- Popup menu for multi-reference bookmarks navigation
- Drag and drop reordering enabled by default
- Cairo color dot in treeview for tagged folders
- Current verse green highlight disabled when tag color present
- Fix bookmark folder labels localization: gettext now initialized
  before default bookmarks are created, so folder names (Personal,
  What must I do to be saved?, etc.) are properly translated on
  first run

Closes #968
Closes #685

Author: lafricain79

po/POTFILES.in

@@ -93,6 +93,7 @@ src/xiphos_html/xiphos_html.c
 ## Glade files
 ui/bookmarks.glade
 [type: gettext/glade]ui/bookmarks.gtkbuilder
+[type: gettext/glade]ui/folder.gtkbuilder
 [type: gettext/glade]ui/editor_link_dialog.gtkbuilder
 ui/editor_note.xml
 ui/editor_studypad.xml