Update gedit3 to 3.20.1

- Use a menubar only if gtk-shell-shows-menubar is set to true
- Spell plugin: adapt code for gspell API changes
- Save window size properly
- CSS updates
- AppData: add project_group and translation tags
- Rename to "Text Editor" in the .desktop file
- Use traditional menubar layout on XFCE, Unity, etc
- require the latest gspell for the spell plugin
- New Windows WiX installer
- CSS updates to track GTK+ changes
- Ship our own app icon
- Add shortcuts window
- Adapt code for gspell API changes
- Rename GeditViewHolder -> GeditViewCentering
- CloseConfirmationDialog: subclass GtkMessageDialog
- CSS updates to track GTK+ changes
- Change default document title to "Untitled Document"
- Port the spell plugin to gspell
- Make the Replace dialog resizable
- Fix close confirmation dialog regression introduced in 3.17.92
- Spell checking: fix performance problem and re-organize the code
- Move minimap settings in the preferences dialog
- CSS improvements
- Add a snippet generating RPM SPEC %changelog line
- gtk-mac-integration support fix
- Add a menu to toggle the source map
- Fix print margins
- Fix the --wait options when passing a list of files
- Improve the Encodings dialog
- Add setting to display a grid pattern
- Misc bugfixes
- Translation updates

(prlw1)