Add SENNA

[valeriobasile]

SENNA (http://ronan.collobert.com/senna/)is a NLP tool that provides, among other things, semantic role labeling. KNEWS uses Boxer for SRL, which it is outdated, not accurate, and not maintained anymore. Try implementing SENNA as an alternative.

[valeriobasile]

Found that SENNA outputs propbank-style semantic roles (arg0, arg1, ...), which can be hard to map to FrameNet roles. Try SEMAFOR instead: http://www.cs.cmu.edu/~ark/SEMAFOR/