Merge readonlyRootfs and development mode into debug mode

The core issue we want to solve is to debug a running app.
Let's make it explicit that it is in debugging mode because
functions like update/backup/restore don't work.

Part of #171

migrations/20170119234504-appdb-add-debugModeJson.js

@@ -0,0 +1,15 @@
+dbm = dbm || require('db-migrate');
+
+exports.up = function(db, callback) {
+    db.runSql('ALTER TABLE apps ADD COLUMN debugModeJson TEXT', function (error) {
+        if (error) console.error(error);
+        callback(error);
+    });
+};
+
+exports.down = function(db, callback) {
+    db.runSql('ALTER TABLE apps DROP COLUMN debugModeJson ', function (error) {
+        if (error) console.error(error);
+        callback(error);
+    });
+};