v19: Mocha MATE

This release features the initial branding for Solus 4.0 Fortitude, MATE Edition. This changes several defaults, such as:

• Default GTK Theme is now Plata-Noir
• Default Wallpaper is The Devil's Bridge from solus-artwork
• Slight increase in default panel size to 28px, easier to use on laptops with higher resolution monitors.

v18

Changelog:

• Change wallpaper to IMG_9656.png for Solus 3.9999
• material: Make the panel slightly transparent
• panel: Add a separator after the clock