Add ability to disable apps and websites while slashing#237

As this is a productivity app, it would be great if, while “slashing”, you could choose to disable apps or websites. For example, disabling Facebook or Slack notifications, and preventing users from being able to access these websites/apps. Of course, this should be configurable so users can manually chose the apps/websites they want to disable, or optionally add a whitelist.

Many of the popular focus apps have this, like https://heyfocus.com/ or https://focusme.com/ for example.