Add URL Input Field in Event Details

[wernerjoss]

Steps to reproduce

Add/edit Event in Calendar Sidebar

Expected behaviour

There should be an URL Input Field in Event Details

Actual behaviour

Currently there is no way to add an URL to an Event

Server configuration

Operating system: Debian Buster

Web server: Apache2

Database: Mysql

PHP version: 7.3

**ownCloud version: 10.5

**Calendar version: 1.6.4