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

src/test/database-test.js

@@ -542,8 +542,7 @@ describe('database', function () {
             altDomain: null,
             xFrameOptions: 'DENY',
             sso: true,
-            readonlyRootfs: true,
-            developmentMode: false
+            debugMode: null
         };
         var APP_1 = {
             id: 'appid-1',
@@ -565,8 +564,7 @@ describe('database', function () {
             altDomain: null,
             xFrameOptions: 'SAMEORIGIN',
             sso: true,
-            readonlyRootfs: true,
-            developmentMode: false
+            debugMode: null
         };
 
         it('add fails due to missing arguments', function () {