The fixture server now supports state substitutions. This allows us to
embed dynamic values in our fixtures.
The `custom-token` fixture has been updated to include such a fixture.
The date that the seed phrase reminder was last shown has been updated
to always be the current date, to prevent the reminder from showing up
during e2e tests. This fixes the e2e test failure for the test
"add-hide-token.spec.js" that we've been seeing on CI lately.