Moved portions from module i18npool, all of former i18nisolang1 library
that now is i18nlangtag. Included are languagetag, isolang and mslangid.

This i18nlangtag code is now even used by module comphelper, so
disentangling i18npool and making this an own module was needed to not
create circular module dependencies.

Change-Id: Ib887c3d6dde667403fd22d382310ba5f1a9b0015