Update pt_BR.ts
Updated Brazilian Portuguese translation by Alexandro Casanova
Tweaks for background color since CSS isolation was introduced
MDict: Narrow selector scope for better CSS isolation (probably)
Fixed #328: Eliminate partially-checked checkboxes in Pereferences

This also eliminates the major problem on Xubunty 13.04 x64, when all those
partially checked checkboxes were without check marks at all.