AGPUSH-504 Adding basic snapshot and restore hooks for upgrading the cartridge

To test it:

1) Create an instance
```
rhc app create --no-git <APP> https://cartreflect-claytondev.rhcloud.com/reflect?github=fjuma/openshift-origin-cartridge-aerogear-push
```

2) Log into the admin console, set your new password, create push applications, create variants, and send some push notifications.

3) Create a snapshot, then delete the instance, then create a new instance and restore it from the snapshot.
```
rhc snapshot save <APP>
rhc app delete <APP>
rhc app create --no-git <APP> https://cartreflect-claytondev.rhcloud.com/reflect?github=fjuma/openshift-origin-cartridge-aerogear-push
rhc snapshot restore <APP> -f /PATH/TO/<APP>.tar.gz
```

4) You should now be able to log into the admin console with the same password you previously set, see existing push applications and variants, and send push notifications.

Note: An 0.11.0 instance is being created in step 1) and step 3) just to simplify testing since we don't have MySQL-specific hooks implemented yet for model changes.