Changed type UUID of Comment.id to String (because key in BasicCache is type String).
Changed type Timestamp of Comment.postTime to java.util.Date (better for hibernate @DateBridge annotation)
Created class UUIDStringGenerator to generate string representation of randomly generated UUID for Comment, Song and Interpret classes.
Implementation of CommentManagerImpl (except quering infinispan).

Signed-off-by: Radek.Koubsky <radekkoubsky@gmail.com>