Move translated files to their own directory

Move translated files to their own directory

What I did:

* move xx_foo.ext to xx/foo.ext

* update Makefile.am to make install work

* minimally update scons_manifest.py (I'd be surprised to see it
  work).

* update i18nLibFileSearch to use the new naming scheme, and keep
  temporarily some code that checks the old method.

* update image paths in .lyx files

* update name of files (examples in tutorial, for ex.) in lyx files

What is definitely broken:

* cmake (did not touch it)

* TOC files (I am not sure how the code works)

I would be surprised if nothing else was wrong.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@17343 a592a061-630c-0410-9148-cb99ea01b6c8