ISIS-568: moving up to JDK 1.7.
ISIS-851: removing isis-module-background (moved back to core-runtime), and updating simpleapp/todoapp to reference 1.6.0 modules directly.

Specifically:
- removed dependencyManagement declarations of the o.a.i.module:isis-module-* Maven modules in core's parent pom.xml, and as <module>s
- moved BackgroundCommandExceution out of isis-module-background and back into isis-core-runtime (so that all modules are optional)
- changed implementation of BackgroundServiceDefault so that no longer fails fast if its prereq dependencies not available (and instead fails only if used).  This means that can now be automatically made available (via @DomainService) with no configuration required.
- in simpleapp & todoapp's root pom.xml now reference isis 1.6.0 core's isis-module-* directly (and by individual version).
- in simpleapp & todoapp's webapp pom.xml, remove dependency on isis-module-background since (will) no longer exist.

In addition:
- in simpleapp, deleted ComponentFactoryRegistrarForSimpleApp, since is a no-op and just adds noise.
- in simpleapp & todoapp's persistor_datanucleus.properties, removed accidental duplication of a property.
- aligned IsisConfigurationForJdoIntegTests (programmatic setup of JDO config props) with that of persistor_datanucleus.properties (file-based setup)
- bumped pom-jdo-enhance-all to 1.7.0-SNAPSHOT
- also fixes to RO TCK (change to fixture data, a bit fragile :-( it would seem...)