[MPlayer-translations] Symbolic constants of GUI help message texts about to be renamed

[Ingo Brückl]

FYI: I'm about to rename the symbolic constants of the GUI help message texts
to create a kind of GUI namespace. This is primarily cosmetic and doesn't
touch the translations themselves.

However, some definitions have been condensed. As a result, we have to deal
with less translations, but on the other hand there may be localized texts
now where formerly an English replacement text has to be chosen, because the
translation was missing. Although I've carefully selected which (few)
definitions should be condensed I cannot guarantee that an existing
translation which will be used now is the best one, but it should be better
than the former English replacement at least.

Example: We had two definitions for "Audio". In the Danish file, one was
translated ("Lyd"), one wasn't. As a result, there were two lables: "Lyd" and
"Audio".
Now, there's only one definition for "Audio" (translated in the Danish file)
and we have two labels both saying "Lyd".

Maybe that's a good opportunity for the translators to have a look at their
file after my commit.

The compiled localized binaries of languages with a high percentage of
translations (cs, de, en, es, fr, hu, it, pl, ru, sk, tr, uk, zh_CN, zh_TW)
have been checked to remain identical by the way.

Ingo