Add more settings

[DarkCat09]

Settings should be placed either below URL bar or on a separate page. Maybe there's no point in the second.

Either pass all the settings (listed below) with the /get txtdot query, which will make txtdot URLs bigger, or save the settings in cookies, so they will be user-specific, which is the intended and handy functionality as I think.

• Proxy images: Remove from page / No proxy / Compress / Original
  see Restrict proxy to media MIMEs, split routes #98 Add image compression #96
• (??) Proxy media, i.e. video & audio
• Replace iframes: Remove from page / No replace / Parse with txtdot

And, of course:

• Dark theme: Off / Auto / On