Bug 1081083 - Add getSelectedCell method in widgets.js. r=aeftimie, r=amatei, r=hskupin

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branch : mozilla-beta
extra : transplant_source : %3C%0B%8B%AE%9D%FF%FB%3Ca%9E%91k%9D%87%01%D6%25%C3%9D%E5