Remove hardcoded credentials from the code

[stepansnigirev]

Currently, access token is hardcoded. We need to have an "AMP login page" when activating the extension.
I think it makes sense to have a login page that supports both username + password and token for login.
Access token can be stored in the user settings similar to Swan and other extensions.

[stepansnigirev]

encrypted file content can be like that:

{
   "liquidv1": "mainnet token",
   "liquidtestnet": "testnet token",
}