Add encryptionVersion to backups

this will identify the old style backups and warn user that a restore
doesn't work anymore

migrations/schema.sql

@@ -121,7 +121,8 @@ CREATE TABLE IF NOT EXISTS appEnvVars(
 CREATE TABLE IF NOT EXISTS backups(
     id VARCHAR(128) NOT NULL,
     creationTime TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
-    version VARCHAR(128) NOT NULL, /* app version or box version */
+    packageVersion VARCHAR(128) NOT NULL, /* app version or box version */
+    encryptionVersion INTEGER, /* when null, unencrypted backup */
     type VARCHAR(16) NOT NULL, /* 'box' or 'app' */
     dependsOn TEXT, /* comma separate list of objects this backup depends on */
     state VARCHAR(16) NOT NULL,