Updated xgettext.py to support the new topic keyword.
Revert "Added topics to dialogs."

This reverts commit 0012a5a5ac4a521abc99e65dfeaafeac0c5d81e2.
Revert "Added topic keyword to Martigan dialogs."

This reverts commit cedd319c3579eadc475e556ed91ffe94dc6c155b.