Initial work towards OPENDJ-1195: Realign the SDK developer guide with the SDK trunk once the new Maven module and package layout has been validated

* convert opendj-ldap-sdk module into a Maven group (pom + only dependencies)
* kept old opendj-ldap-sdk site as primary "About" page in order to avoid breaking bookmarks and links. The opendj-core module's site is hidden
* remove all sub-module site.xml files and instead inherit menus from parent
* switch SDK Javadoc URLs to point at opendj-core Javadoc since opendj-ldap-sdk Javadoc is stale
* add simple place holder index.xml.vm site pages for most sub-modules
* change how we document getting the binaries: instead reference the dependencies report. Although slight less helpful to the reader, at least the links won't become stale.