Icedove wrapper is not integrated in our i18n system

I see gettext commands in the script but the strings are not in our PO files. See refresh-translations and po/POTFILES.in. Once done, I suggest translating a string and checking that it indeed appears translated in the UI.

Feature Branch: kytv/bugfix/10756/icedove-po

Parent Task: #5663 (closed)

Original created by @intrigeri on 10756 (Redmine)

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