Jdk11 support

[jarlesat]

Three changes:
Building using JDK8.
Upgrades asm to version 7.0, being able to read classes built in JDK11.
Slightly better stacktrace from MessageExtractorException

[jhorstmann]

Thanks for the contribution! As you can see I haven't touched this project in quite some time but it's great to see someone still using it.

Do you think it would be possible to already throw the MessageExtractorException with the file name / systemId in the message? From a quick look through github this name should be available when throwing and we don't need to wrap the exception in another layer.

[jarlesat]

I have force pushed a change. I did not see that the filename was available in the InputStream as systemId. In fact I added the filename as a message, because there were an error in two EL-expressions in one of my xhtml-files that I could not see, and JSF has silently accepted for a couple of years. I am testing to see how easy it is to swap out properties-files with po-files.