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.
Do we need the:
> If the collection does not exist, a new collection is created.
Its confusing as to why you would use this if the collection does exist and doesn't answer what happens if you have different options (eg capped)