Don't set new pallete but match best fit theme

[Emaleth]

Problem with pywal is that regardless of the back-end used, sometimes colors are just not great. And so, how about adding an option which does the following:

• Generate palette (as usual)
• Look trough built in themes and set the best match

Yes, this would mean that calling wal -i /path/to/wallpaper doesn't necessarily change the theme but it sets the new wallpaper and guarantees the best match. Sort of base16 powered reliability.

[Emaleth]

didn't notice duplicate: #589