[DS] Control felix optional extensions through xml attributes in component descriptor

Currently the felix optional extensions are controlled either through a global property or through a felix namespace for the component description xml. I'm going to introduce a namespace (I propose "http://felix.apache.org/xmlns/scr/extensions/v1.0.0") and attribute names to control these per component in a normal DS namespace. These will be easy to add using a bnd annotation (not yet committed, but soon). The attribute names I have so far are:
configurableServiceProperties (cf FELIX-4149)
persistentFactoryComponent (no issue yet)
deleteCallsModify (cf FELIX-2523)
obsoleteFactoryComponentFactory (per-component version of global ds.factory.enabled property)
configureWithInterfaces (no issue yet, allow interfaces as well as annotations to configure 1.3 components)
delayedKeepInstances (per-component version of global ds.delayed.keepInstances property)