Add "gettext-domain", "extension-id" (containing the base part of the
UUID) and "gschemabase" (which, combined with "extension-id", gives
the GSettings schema) to metadata.json, autogenerated by the build
system.
Now, typing "make zip-file" will create a standard zip-file for each
extension, with everything necessary, including translations and GSettings schemas.
These files can then be installed with the tweak-tool or uploaded
at extensions.gnome.org
Based on an earlier patch by Jasper St. Pierre.
