Get Help building again.

1. <!ENTITY app "GnuCash"> was missing in all languages
2. in de/gnucash-help files were renamed, but neither in the makefile nor the files themself 

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash-docs/trunk@23651 57a11ea4-9604-0410-9ed3-97b8803252fd