Minor changes

• Added Xfce support
• Improved assets for a better match with the global dark theme.

Patches

• Fixed deprecated methods (#17)
• Fixed blurry icons (#26)
• Fixed gnome shell issues in 3.26
• Fixed hover indication on popovers (#28)
• Fixed blacked emojis on gnome shell notifications
• Fixed focus state on gnome-shell buttons
• Fixed selected items in inactive window (#35)