pantheon.gala: 2019-02-09 -> 2019-05-14

Fixes notification settings being broken[0] and
many other things. See the changes[1]

[0]: https://github.com/elementary/switchboard-plug-notifications/issues/41
[1]: https://github.com/elementary/gala/compare/1a96644c6aac405927499dacb308dea13512e919..3ae100da4bbd9dabe353f468778ef63ef2dcd5d7