Cookie banner enhancement

[tang2087]

Change cookie banner to follow the new asp.net core 2.x standard:

`@using Microsoft.AspNetCore.Http.Features

@{
var consentFeature = Context.Features.Get();
var showBanner = !consentFeature?.CanTrack ?? false;
var cookieString = consentFeature?.CreateConsentCookie();
}

@if (showBanner)
{

Toggle cookie consent banner

Use this space to summarize your privacy and cookie use policy.

Learn More
Accept

<script>
(function () {
document.querySelector("#cookieConsent button[data-cookie-string]").addEventListener("click", function (el) {
document.cookie = el.target.dataset.cookieString;
document.querySelector("#cookieConsent").classList.add("hidden");
}, false);
})();
</script>
}`