Checkpoint commit for OPENDJ-175: Decouple OpenDJ LDAP SDK from Grizzly

* Introduce two new maven modules, resulting from splitting functionality of module opendj-ldap-sdk :
    opendj-core : core APIs
    opendj-grizzly : implementation classes for Grizzly transport provider
    
These modules produce a jar with the same name (opendj-core and opendj-grizzly)
  
The opendj-ldap-sdk module is kept for compatibility. It contains no more source code, 
but it provides a opendj-ldap-sdk jar built from the two new maven modules.

* Move classes in opendj-grizzly module to org.forgerock.opendj.grizzly package
   
* Move some classes in opendj-core module to the org.forgerock.opendj.ldap.spi package 
   Modify visibility of  some constructors and methods of these classes to allow use by classes in opendj-grizzly
   Classes :
     - AbstractLDAPFutureResultImpl
     - LDAPFutureResultImpl
     - LDAPSearchFutureResultImpl
     - LDAPBindFutureResultImpl
     - LDAPCompareFutureResultImpl
     - LDAPExtendedFutureResultImpl

* Duplicated methods in opendj-grizzly module 
  - LDAPReader#decodeEntry
  - LDAPWriter#encodeEntry 
  to methods in opendj-core module
  - LDAPUtils#encodeSearchResultEntry
  - LDAPUtils#decodeSearchResultEntry 
to avoid sharing  or exposing too much code from these classes.