Azote 1.7.8

• styling clicked palette button with button#color-btn-selected added (for colour-blind people like myself);
• colour picker: colour image converted into the Gtk.ColorButton class, to allow the colour edition;
• added tracking the currently selected wallpapers folder for file addition / deletion: switchable, configurable (every 5 sec by default);
• tray status icon added, i.a. to indicate the tracking on/off state;
• python-send2trash from now on recommended as an obligatory dependency.