<issue_start><issue_comment>Title: Add themes; add favicon
username_0: Howdy, 

This PR adds a theme previewer to leftwm.org. It would be nice (tagging leftwm/leftwm-theme#33) if the JSON could be automatically regenerated when leftwm/leftwm-community-themes is updated.


![Screenshot 2021-09-24 at 22-54-30 LeftWM - A tiling window manager for Adventurers](https://user-images.githubusercontent.com/2220164/134757032-1b59bcdb-0ac2-4946-89a8-a57e6a9af8df.png)

![Screenshot 2021-09-24 at 22-54-48 LeftWM - A tiling window manager for Adventurers](https://user-images.githubusercontent.com/2220164/134757031-7034f2b7-e259-42f2-87ec-25761bfff0a7.png)


Best,
Mautamu
<issue_comment>username_0: Bumping.