Add field to skip backup for an app

This skips the app from a backup when doing a full box backup and
simply reuses the previous backup.

The app can still be explicitly backed up using 'cloudron backup'
and explicitly restored using 'cloudron restore --backup'.

When restoring the box, it all depends on the app's last backup.

Fixes #311

src/apps.js

@@ -415,6 +415,7 @@ function install(data, auditSource, callback) {
         sso = 'sso' in data ? data.sso : null,
         debugMode = data.debugMode || null,
         robotsTxt = data.robotsTxt || null,
+        enableBackup = 'enableBackup' in data ? data.enableBackup : true,
         backupId = data.backupId || null;
 
     assert(data.appStoreId || data.manifest); // atleast one of them is required
@@ -484,7 +485,8 @@ function install(data, auditSource, callback) {
                 sso: sso,
                 debugMode: debugMode,
                 mailboxName: (location ? location : manifest.title.toLowerCase().replace(/[^a-zA-Z0-9]/g, '')) + '.app',
-                lastBackupId: backupId
+                lastBackupId: backupId,
+                enableBackup: enableBackup
             };
 
             appdb.add(appId, appStoreId, manifest, location, portBindings, data, function (error) {
@@ -583,6 +585,8 @@ function configure(appId, data, auditSource, callback) {
             }
         }
 
+        if ('enableBackup' in data) values.enableBackup = data.enableBackup;
+
         values.oldConfig = getAppConfig(app);
 
         debug('Will configure app with id:%s values:%j', appId, values);