JAVA-1410: Javadoc for legacy API

Made a first pass through the com.mongodb package and the existing API classes.  I've added some jira tickets for missing tests and code we might be able to delete, and updated the [Jira ticket](https://jira.mongodb.org/browse/JAVA-1410) with the classes that I couldn't document without help.
This is not true.  It doesn't create a collection on the server.  It just creates a client representation of the collection that can be used to interact with the server.

Also, not sure what that comment about being NOT part of the public API means?  DBCollection is part of the public API.  Does it mean that this method is not?  I think it should just be removed, since we're not deprecating it in 2.x.