fix(binding): fix international value binding

[masonlouchart]

Before this commit, the property internationalValue was only one-way binding. Others elements watching this value were not aware of the changes. Now the gold-element-input is using two-way binding on this property so parents are notified about the changes.

Fixes #83

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[masonlouchart]

I signed it! (and rewrote the commit with proper email address).

[masonlouchart]

With the notify attribute: