New Plugin: Sync 

Use Google Realtime API to store key value pair in CollaborativeMap. Allow other plugins to sync data between client.

Other plugins can using following 2 function to register for syncing and push update. Refer to source code for detail.
`window.plugin.sync.registerMapForSync(pluginName, fieldName, callback, initializedCallback)`
`window.plugin.sync.updateMap(pluginName, fieldName, keyArray)`