describe translation strings better

One of our translators (@dreadk2002) has asked to get better description on some of the strings we have. Possibly I'll add more to this commit as he/she works through all our strings.

Also, is `FRONT` and `REAR` not used anymore by core?

    git grep "Lang::FRONT" $(git rev-list --all) 

Suggests it was used in `ShipType.cpp` but all commit hashes are wrong. Or I am? Remove them? Unused strings aught to be removed.