Add website to exception list when updating the rate of pay

[raducristianpopa]

Context

Users have the ability to change the rate of pay for each website.

Todos

• Add debounce for the rate of pay slider;
• After changing the rate of pay, send the updated amount to the background script, convert the amount to the asset scale of the wallet (represented as a string, eg: asset code USD, asset scale 2, amount 0.01 -> amount * 10 ** scale) and add the website in the exception list using the below format;
• If the website is already in the exception list, only update the amount (after converting it as well);

Format

{
  "exceptionList": {
    "https://example.com": {
      "amount": "60", 
      "interval": "3600000" // in ms
    }
  }
}

The interval property is for future proofing. For now, we will only store the default value for the interval, 1 hour in milliseconds.