Added a new Subscription tab where users can login with their Studio platform account. This enables you to use the plugin with an associated paid Studio platform plan.

Note that this does not change anything for users who have an existing license key or purchase a new plugin license key, that still can be managed and accessed from https://account.tokens.studio/ and can still be entered in the license key field on the Subscription tab. We're consolidating the two systems in the future.

This sets the basis for a more streamlined account management system that we’re working towards.