Write the grounded MLN to a file

@ashish33 @niranjanb 

Added a "-writeClauses <file>" option to print out the grounded MLN with original predicate names and domain constants, e.g.,

!E_barrons_rule2661_3("Var1") v Example("Var1", "Var1") v !IsaEn("Var1", "Gravity")
IsaEv("Var4", "a force") v !IsaEv("Var4", "the force")
!E_barrons_rule1530_1("Var6") v Example("Var1", "Var6") v !IsaEn("Var1", "Gravity")