[bd] Paygate: STRIPE

[FEATURES]
1. Add support for Stripe as a pay gate
2. Accept subscription

[INSTALLATION]
*. You must have [bd] Paygates installed.
1. Upload the library directory into your XenForo's
2. Import the add-on
3. Configure pay gate options in AdminCP > Options > [bd] Paygate: STRIPE
4. Configure Webhook for your account at https://dashboard.stripe.com/account/webhooks to use this url: http://domain.com/xenforo/bdpaygate/callback.php?p=stripe (only if you want to use recurring payments)