If a website has a Service Worker installed it would load and register before a User tries to login to the backend causing a "Invalid security token" message. This PR unregisters any installed Service Worker when a User opens the backend Signin webpage.
I have also added the NEW Security Headers to add Protection to October's Cache and Cookies. This includes two new Middleware that first clears any bad cached data before a User tries to login and the second Middleware will clear all the sensitive User Data when a User signs out of the Backend.
For more info on the new Security Header 'Clear Site Data' you can see the spec found here: https://www.w3.org/TR/clear-site-data/Fixes#4076, fixes#3707.
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