Extract comments for translators

[aBlueShadow]

This enables the add-comment option in gettext, that allows scenario writers and c++ coders to give translators detailed information about a given text.

Example how it works:

Right before the line that contains a translation string, add a comment that contains the TRANSLATORS keyword (case matters)

-- TRANSLATORS: F is formation spacing of the drones, S is their scan range
addGMFunction(string.format(_("buttonGM", "+Distance F%.1fU S%.1fU"),drone_formation_spacing/1000,drone_scan_range_for_flags/1000),setDroneDistances)

After the update/creation of the base translation files, that comment now got added to the .po file, which will look like this in Poedit: