Bug 670872 — Should be less sensitive to accentuated chars

Strip accented characters from names and make them all lower case when
searching for potential matches between individuals.

This uses a modified version of Empathy's live search code to allow for
string matches regardless of case or accentuation.

The commit also fixes the potential match code to handle UTF-8 properly,
which it wasn't doing before.

This includes a test case.

Closes: https://bugzilla.gnome.org/show_bug.cgi?id=670872