Merge pull request #4431 from metabase/set-site-url-via-middleware

frontend/src/metabase/admin/settings/selectors.js

src/metabase/api/session.clj

src/metabase/api/setup.clj

src/metabase/core.clj

src/metabase/db/migrations.clj

src/metabase/email/messages.clj

src/metabase/middleware.clj

src/metabase/models/user.clj

src/metabase/public_settings.clj

src/metabase/query_processor.clj

src/metabase/util/embed.clj

src/metabase/util/urls.clj

test/metabase/publc_settings_test.clj

test_resources/log4j.properties