Add more configuration options

Simple configuration page. Minumum configuration that will be available:

Twitter:

• Disable retweets.
• Disable loading images (show link instead)
• Show tweet stadistics (slower rendering)

Youtube:

• Disable thumbnails.
• Specify default video quality

General:

• Dark mode.
• Change password.
• Export data to JSON.
• Import data from JSON.
• Delete account.
• Instance information.
  • Total instance users.
  • Instance location.
  • Instance name.