Double Stored Cross-Site scripting in the admin panel

##Description Hello. I discovered a Stored XSS attack vector in the `Custom Domain` field ##POC & Reproduction steps 1. Login to the federalist and go to the some instance `http://localhost:1337/sites/<siteid>/settings` 2. Fill the `Custom Domain` field by the ``` blocked:alert(document.domain) ``` and `Demo domain` ``` blocked:alert(document.domain); ``` (it cannot be the same so we bypass the check by adding `;`) 3. Save and press `View Website` button. You will be XSSed. {F199337} {F199336} 4) Go to the `http://localhost:1337/sites/<siteid>/published` - and press view on the demo site to test second Stored XSS {F199338} ##The impact The XSS requires user interaction (e.g. clicking the button). But still, it is a bad thing. Anyone who gain access here, can conduct stored XSS attack against other admins. ##The root cause & suggested fix The input fields not sanitized properly - it should allow only alphanumeric characters, and dots.