Do some housekeeping related to reporting of license information.

Background: from a layman's POV, WildFly Core is an LGPL 2.1 project (since it contains lots of LGPL 2.1 code) but we would like at some point to make it ASL 2. To further that, new code for a long time now has had ASL 2.0 file headers, and we have reviewed the LGPL 2.1 code and feel we could convert the headers on those to ASL 2 when we have time. Component dependencies are another matter, but are not directly relevant to this issue.

So, we have a mix of code, some with LGPL 2.1 and some with ASL 2.0. Per our understanding we are meant to report both licenses in "automated" reporting locations like the project root pom.xml and the core-feature-pack-licenses.xml file. This fix will do that.

Also, we want to ship a LICENSE.txt file that includes the formal license text referred to in the file headers. That's just good practice for any OSS project. Since files refer to both LGPL 2.1 and ASL 2, the file will include the text from both.

Finally, the pom.xml and the core-feature-pack-licenses.xml file will refer to LGPL 2.1 "or later" rather than "only" as that is the typical way LPGL is handled and it conforms with what is said in the file headers.