etc: add flash player config
etc: add X11 config rule to force enable touchpad tapping
skel, data: add default wallpapers, update xscreensaver image path and default xfdesktop wallpaper
usr: add lightdm-gtk-greeter tweaks
usr: add startpage and duckduckgo as synapse search engines
usr: add ffmpegthubnailer as default thumbnailer for videos
usr: add xfce4-terminal colorschemes