This change updates a few more dependencies, and gets rid of some things that we actually don't need: - Passport has been updated to the latest, and the slack stragegy has been switched over to a different implementation which is actually being maintained. - Changed to importing the standalone build for selectize, which lets us get rid of the explicit `sifter` dependency. `sifter` was depending on some vulnerable versions of other libraries. The standalone Selectize bundles a newer version of selectize which doesn't have this problem. - The published versions of scss libraries have some security problems. We're not importing any SCSS files, so all of this can just go away. - We're no longer using gulp-shell at all. Testing Done: Verified that login/logout still worked correctly. Checked build and basic functionality.