Wire-in new BEL Script grammar

[nbargnesi]

Wire-in new BEL Script grammar (BELScript_v1.g and BELScriptWalkWalker_v1.g) to the editor. Each document should support an AST model.

[nbargnesi]

My belscript-grammar repository contains examples for building and using the BELScript_v1.g grammar.