[nemo-qml-plugin-contacts] Move number de-duplication logic into SeasidePerson
[nemo-qml-plugin-contacts] Allow extended numbers through de-duplication

When removing duplicate numbers, allow the longest form of a number
to be retained provided it is longer than any initial-plus variant
of the number.  This is specifically to allow numbers that have been
prefixed with codes that select an alternative telephony provider
to be passed through duplicate removal.
Merge pull request #80 from matthewvogt/extended-numbers

[nemo-qml-plugin-contacts] Allow extended numbers through de-duplication