Use gsettings instead of X resource database

Use gsettings instead of X resource database

* src/pgtkfns.c (pgtk_is_lower_char, pgtk_is_upper_char)
(pgtk_is_numeric_char, parse_resource_key)
(pgtk_get_defaults_value, pgtk_set_defaults_value)
(Fpgtk_set_resource, pgtk_get_string_resource): handle gsettings scheme

* m4/gsettings.m4: new file

* etc/org.gnu.emacs.defaults.gschema.xml: new file

* configure.ac (GLIB_DISABLE_DEPRECATION_WARNINGS)
(gsettingsschemadir):

* Makefile.in (gsettingsschemadir, GLIB_COMPILE_SCHEMAS)
(install, uninstall, clean):

* .gitignore: add gschema

*.gschema.valid は生成ファイルなので無視。

schema の置き場所を変更。