New UVL reader is very inefficient

[jmhorcas]

The last update of the UVLReader makes the loading of the feature model too slow comparing with the previous version.
In fact, I am testing it with the linux-2.6.33.3_simple model and it is never ends of reading the file.

[jagalindo]

Well, that's the official uvl parser written in antlr4. Note that the current parser supports all the elements, making it slower. IMHO, for compatibility this one should be used, otherwise we could try to implement a lark parser.