Use uberfire.version property to define version of uberfire-bom

I tried to capture the need for this change in the comment in ubefire-parent-with-deps/pom.xml. It is a bit tricky issue to explain, so in case something is not clear, please let me know and I can answer your questions.

Would it be possible to forward port this also into master, so we don't have to deal with this problem in future, when using more recent version of uberfire?