Extend the LogManager to support -get <lineNum> <field list>

Based on the Gora API, the Gora backend datastore modules should provide an implementation of the method get(K key, String[] fields). This is a very useful and important method of the Gora API. However, the tutorial sample application LogManager does not demonstrate this functionality. Currently it only has an option to fetch an object based on its key, which calls the get(K key) method that fetches all the fields. I propose to extend the LogManager options and provide a new option as follows:
-get <lineNum> <field list>
This would call the datastore.get(K key, String[] fields).

I believe that it is important to demonstrate this Gora functionality in the official tutorial application.