1) Introduces apps/features.txt that controls which strings are included
for each target based on defines.
2) .lng and .voice files are now target specific and the format versions
of both these file types have been bumped, which means that new voice
files are needed.
3) Use the 'features' mechanism to exclude strings for targets that
didn't use them.
4) Delete unused and deprecated and duplicated strings, sort strings in
english.lang
Some string IDs were changed so translations will be slightly worse than
before.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@14198 a1c6a512-1295-4272-9138-f99709370657
