Feature: add compatibilty with pure text address field.

The address field of an event created within Mobilizon currently has the context https://schema.org/address. The types from schema.org could be either a PostalAddress or pure Text. Mobilizon always uses the PostalAddress. This is fine as the GUI works like that.

But when parsing an incoming event from another non-Mobilizon instance it does not map a pure text address field in any way to its internal data structure. The information just gets lost. It would be awesome, if Mobilizon would still handle an address of type text.

Having the name of the location and the address seperate can have a lot of advantages, also when it comes to how Mobilizon displays events on the overview pages, compared to just having a single text field for both.

Gancio already made a design decision in that way and many WordPress Event Plugins don't have more seperated information available either.