Cleanup and improve environment properties

The Environment class should use the same property names as the template mechanism.
We should have a single property model.
This may affect tomcat and jetty launchers (may be client launchers too) so all the other distributions should be tested for regressions.

These are standard system properties that are must be set on any Nuxeo distribution:
(the system properties are usually set by deployers or bootstrap code)

public static String NUXEO_HOME_DIR = "nuxeo.home.dir";

public static String NUXEO_DATA_DIR = "nuxeo.data.dir";

public static String NUXEO_LOG_DIR = "nuxeo.log.dir";

public static String NUXEO_TMP_DIR = "nuxeo.tmp.dir";

public static String NUXEO_CONFIG_DIR = "nuxeo.config.dir";

public static String NUXEO_WEB_DIR = "nuxeo.web.dir";

"nuxeo.host.name",
"nuxeo.host.version"

On specific distributions you may have additional properties like "nuxeo.ear.dir" on JBoss5.