Validate duplicated addresses in the address book and settings

[francovenica]

It was reported in the #1666 because I thought it was all the same problem, but it seems is not

Steps
In the address book, Create an entry and save it
Create a new one and input the same address as the last time.

In the settings
Add or replace an owner
In the address input enter the address of one of the owners

Outcome:
The address is taken as valid by the input and I can submit the form

Expected
Is expected that the input shows an error message for duplicated address and the submit button should not be available

Address book:

Settings: Adding owner (same happens for owner replacement)

[tschubotz]

marking this as major as I assume people rely on the address book for verifying addresses and this can be confusing.