Factor out addresses into their own model

Addresses could be stored as a complex data type with correct validation.

mentioned in commit 30d2455a

added workflow::discussing label

changed due date to January 24, 2020

removed due date

assigned to @nik

changed milestone to %2.0a1

added workflow::confirmed label and removed workflow::discussing label

Decision by dev meeting: Do so.

changed milestone to %2.0a2

unassigned @nik

added workflow::confirmed label

changed title from Complex data types for addresses and phone numbers to Complex data types for addresses

changed the description

assigned to @debdolph

added part::backend prio::2 type::feature labels

removed milestone

removed milestone

unassigned @debdolph