Add copyright notices in several files.

Add copyright notices in several files.

Reported by <ineiev@gnu.org> in <https://savannah.gnu.org/bugs/?54809>.

* gettext-tools/doc/FAQ.html: Fix copyright notice added on 2019-04-04.
* gettext-tools/doc/tutorial.html: Add GFDL copyright notice. Permission given
by Gora Mohanty <gora_mohanty@yahoo.co.in> through private email on 2004-11-13.
* gettext-tools/po/Makevars.template: Don't mention the file name, since this
file is meant to be copied and renamed to 'Makevars'.
* gettext-tools/examples/hello-*/po/Makevars: Add all-permissive copyright
notice.
* gettext-tools/examples/hello-c-gnome3/hello.ui: Add public-domain notice.
* gettext-tools/examples/hello-c-gnome3/hello.gresource.xml: Likewise.
* gettext-tools/examples/hello-c-gnome3/hello.gschema.xml: Likewise.
* gettext-tools/examples/hello-java-awt/m4/TestAWT.java: Likewise.
* gettext-tools/examples/hello-java-swing/m4/TestAWT.java: Likewise.
* gettext-tools/examples/hello-java-qtjambi/m4/Test15.java: Likewise.
* gettext-tools/examples/check-examples: Add GPLv3+ copyright notice.
* gettext-tools/examples/installpaths.in: Likewise.
* gettext-tools/examples/po/mmsmallpo.sh: Likewise.
* gettext-tools/examples/po/xsmallpot.sh: Likewise.
* gettext-tools/its/glade.loc: Likewise.
* gettext-tools/its/gsettings.loc: Likewise.
* gettext-tools/its/metainfo.its: Likewise.
* gettext-tools/its/metainfo.loc: Likewise.
* gettext-tools/src/filters.h: Add missing copyright line.