Globally configurable number of extender threads and grace period timeout

At Seeburger AG we migrated from JBoss to Karaf. We use Aries modules for transaction capable beans. Since the migration, the number of blueprint bundles increased and we started to get errors of this kind:

org.apache.aries.blueprint.container.BlueprintContainerImpl	 JB2688	 Blueprint Extender: 1	 B6AIO1@b6aio1bd4ef	 ERROR	 	 	 	 	 Unable to start blueprint container for bundle com.seeburger.portal.backend/2.55.0 due to unresolved dependencies [(objectClass=javax.transaction.TransactionSynchronizationRegistry)]
@LGW800	2018-07-04T12:01:36.637+0200

So we tried to increase the number of extender threads and grace period timeout in our blueprint fork to fix it. We introduced this in our master branch in July 2018 and it increased the stability of our software. This is why we want to propose this change also to be done in aries, which can be reviewed in PR91