XLS Decision table: Add support for a boolean column indicating that the row (rule) should be negated

Add a boolean column to the XLS decision table parser to allow rules to be negated:-

When "turned on" for a rule:-

when
not (
pattern1..
pattern2..
)
then
...
end

When "turned off" for a rule:-

when
pattern1..
pattern2..
then
...
end