Ditch dbmate in favour of internal migration

such that migration files can be embedded

backend/internal/database/migrations/20201013035839_initial_data.sql

@@ -0,0 +1,38 @@
+-- migrate:up
+
+-- Default error reporting setting
+INSERT INTO `setting` (
+	created_on,
+	modified_on,
+	name,
+	value
+) VALUES (
+	strftime('%s', 'now'),
+	strftime('%s', 'now'),
+	"error-reporting",
+	"true"
+);
+
+-- Default Certificate Authorities
+
+INSERT INTO `certificate_authority` (
+	created_on,
+	modified_on,
+	name,
+	acme2_url
+) VALUES (
+	strftime('%s', 'now'),
+	strftime('%s', 'now'),
+	"Let's Encrypt",
+	"https://acme-v02.api.letsencrypt.org/directory"
+), (
+	strftime('%s', 'now'),
+	strftime('%s', 'now'),
+	"Let's Encrypt (Staging)",
+	"https://acme-staging-v02.api.letsencrypt.org/directory"
+);
+
+
+-- migrate:down
+
+-- Not allowed to go down from initial