xgettext: Rewrite Glade scanner in ITS

xgettext: Rewrite Glade scanner in ITS

* gettext-tools/its/glade.loc: New file.
* gettext-tools/its/glade1.its: New file.
* gettext-tools/its/glade2.its: New file.
* gettext-tools/its/gtkbuilder.its: New file.
* gettext-tools/its/Makefile.am (dist_its_DATA): Add new files.
* gettext-tools/src/Makefile.am (xgettext_SOURCES): Remove x-glade.c.
* gettext-tools/src/x-glade.c: Remove.
* gettext-tools/src/x-glade.h (EXTENSIONS_GLADE): Set language field to
NULL.
(SCANNERS_GLADE): Set func field to NULL.
* gettext-tools/po/POTFILES.in: Remove x-glade.c