Checklist

• I made sure that there are no existing issues - open or closed - to which I could contribute my information.
• I have read the FAQ and my problem isn't listed.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Is your feature request related to a problem? Please describe.
At the moment there is only a single field for addresses. Therefore addresses are not synced correctly when also syncing with other clients like Thunderbird which have structured address field support.

Describe the solution you'd like
Add individual fields for the different address parts. Could be done as an option to support simple mode also for people who preferre this.

Describe alternatives you've considered
The different fields could be merged into one during sync. This would not improve editing behavior.

Additional context
This fork of Simple Contacts already contains structured address fields and I think the author would be willing to contribute.
https://github.com/stephanritscher/Simple-Contacts