Refactor unregister address method

[fvictorio]

Closes #149. Closes #155.

Note that this will do an unnecessary assignment when the user removes the last address, but I'm not sure if adding a conditional is worth it.

I also added more tests to be sure that it's working as expected.

[coveralls]

Pull Request Test Coverage Report for Build 478

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 79.423%

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Totals
Change from base Build 470:	0.04%
Covered Lines:	961
Relevant Lines:	1185

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💛 - Coveralls

[phahulin]

I think we should add conditional for clarity.

[fvictorio]

Done. I also fixed the issue with the coverage script.