Add link for online meeting directly under event location

[osmers]

Motivation

Some events take place online - right now we use the checkbox that this event does not have a location and add the link to the description.

Proposed Solution

Instead it would be easier to add the link to a link field that appears when checking the box "event has no location". Maybe rename the box to "event has no physical location"

Alternatives

Keep it, as it is

User Story

As an Integreat App user I want to directly see that the event takes place online and not have to look for the link in the description