Add basic end-to-bridge encryption support

Still missing persisting sync tokens and crypto state in DB

database/upgrades/2020-05-09-add-portal-encrypted-field.go

@@ -0,0 +1,12 @@
+package upgrades
+
+import (
+	"database/sql"
+)
+
+func init() {
+	upgrades[12] = upgrade{"Add encryption status to portal table", func(tx *sql.Tx, ctx context) error {
+		_, err := tx.Exec(`ALTER TABLE portal ADD COLUMN encrypted BOOLEAN NOT NULL DEFAULT false`)
+		return err
+	}}
+}