Add translations to notenames plugin

moving it into a folder of it own for this.

Remove superfluos generation of .pro files during realease step, they
are generated in the lupdate step and only used there.

Add a single file containing all supported locales and simply the
build/gen-*-projectfile* scripts to use this single source
Note 1: there's a difference in gen-qt-procectfile* v.s the others in
additionaly having an *_en.ts file
Note 2: in the bat files a hardcoded "..\" is used to find the locale
file whereas in the Shell-scripts "`basename $0`" is used. Is there such a
thing for .bat files too?
Note 3: the .bat files have been tested, the shell-scripts have not been
tested, although they should work.
Esp. the nested "`cmd ... \`cmd ...\` ...`" needs testing, using
"$(cmd ... $(cmd ...) ...)" would be much nicer, but is not available in
plain Bourne Shell
Note 4: the mechnism for plugins searches strings in qml and js files.
QML allows to call js files from withing a qml file, not sure whether
MuseScore supports that too, needs some checking. QML also allows to call
qml files from within a qml file, but MuseScore's Plugin Manager then
lists that other qml file as a plugin too. It doesn't load it though.

Adjust share/locale/Readme.md to above changes