Buff Shortcuts

• Create ui file for ShortcutRow
• Remove dummy data from shortcuts list
• Implement "Reset All" shortctus button - fixes #211 (closed)
• Implement "Reset" individual keybindings - fixes #211 (closed)
• Implement "Add Keybinding" that does not overwrite previous keybindings - fixes #212 (closed), #213 (closed)
• Implement "Remove" individual keybinding
• Add workaround for GNOME/vala#626 in Keymap.apply - closes !74 (closed)