[JAVA-1391] Javadoc for com.mongodb.binding & com.mongodb.connection packages (added missing Javadoc).
[JAVA-1410] Javadoc for com.mongodb package. All missing Javadoc covered except for DBEncoder/Decoder-related classes; some gradle changes to prevent errors with the javadoc check.
Ensure next() and hasNext() behaviour doesn't change

JAVA-1255