Don't require log4j-core for o.e.passage.lic.base

[HannesWell]

At the moment the Plug-in org.eclipse.passage.lic.base imports the package org.apache.logging.log4j.core.config because it uses classes from it in the class org.eclipse.passage.lic.internal.base.logging.Logging.
This causes problem for those that don't want to use log4j-2 as logging framework implementation in their application. In such cases one uses a bridge bundle that redirect all calls to the log4j-2 API to the actually used Logging-framwork implementation, for example logback. There are corresponding bundles for that and that works fine.
But the package org.apache.logging.log4j.core.config is not part of the log4j.api bundle but only of the log4j.core bundle (both are from Maven-Central, not from Eclipse-Orbit, which is a modified form). Therefore o.e.passage.lic.base requires log4j.core even if that is not used in the corresponding application and o.e.passage.lic.base is required by many other Passage plugins, which then transitivly pull in log4j too.

Therefore I want to ask you to make log4j-core not a required for o.e.passage.lic.base anymore.
Currently I can think about two ways how this could be achieved:

• Make Package-Import org.apache.logging.log4j.core.config optional in the Manifest.
  Then o.e.passage.lic.base is only wired to log4j-core, if another Plug-in or Feature with a non-optional requirement adds it to the application but it does not pull in log4j-core into apps launched from the IDE or build by Tycho/P2.
• Move the Logging class to a less basic Plug-in and remove the package-import entirely from passage.lic.base
  Maybe o.e.passage.lic.execute, which also uses it and can export it to o.e.passage.loc.operator.seal.
  But for the use in org.eclipse.passage.lic.jetty the class either has to be copied or the latter plug-in also has to depend on passage.lic.execute, but I don't know if that is wanted.

I can provide a PR implementing the approach you prefer.

[HannesWell]

Fixed by #1140