RenamerDialog: cleanup and Gtk4 prep

[danirabbit]

• Bump copyright header
• Code style
• Use child property where relevant
• Create buttons with labels and icons in a Gtk4 friendly way
• Fix menu appearance for suffix and prefix menubuttons
• Set revealer transitions so they preserve space correctly
• Remove keypress handler for REJECT. It doesn't appear that anything listens to this response ID
• Replace grids with boxes
• Pack boxes with add where relevant
• Fix margins, aligns, expands, etc
• Use MenuButton for mod_button
• Reduce minimum usable width

[jeremypw]

Code looks good. There are a few minor issues involving some buttons needing to be pressed more than once to work but these are also present in main and outside scope of this PR.