OPENDJ-2871 Add support for sub-resources and inheritance

* Rest2Ldap - is now instantiable and is the entry point for configuring
Rest2Ldap data models. Options are injected via the commons Options
class, resources types are defined using the Resource class, and their
relationships with other resources are defined using SubResources. There
is documentation describing the construction process in the Rest2Ldap
class

* Rest2LdapJsonConfigurator - entry point for constructing Rest2Ldap
instances from JSON configuration. Used by the gateway

* TypePropertyMapper - a new attribute mapper responsible for mapping
LDAP object classes to a JSON "type" field

* ObjectPropertyMapper - now supports a "default" attribute mapping mode
(OPENDJ-3100)

* Renamed all AttributeMappers to PropertyMappers to reflect change in
terminology ("properties" instead of "attributes") which more closely
reflects the terminology used in JSON schema and FR API descriptors

* Minor misc changes, e.g. converting classes/methods to camel-case.